view keyimport.c @ 1306:34e6127ef02e

merge fixes from PuTTY import.c toint() from misc.c (revids are from hggit conversion) changeset: 4620:60a336a6c85c user: Simon Tatham <[email protected]> date: Thu Feb 25 20:26:33 2016 +0000 files: import.c description: Fix potential segfaults in reading OpenSSH's ASN.1 key format. The length coming back from ber_read_id_len might have overflowed, so treat it as potentially negative. Also, while I'm here, accumulate it inside ber_read_id_len as an unsigned, so as to avoid undefined behaviour on integer overflow, and toint() it before return. Thanks to Hanno Böck for spotting this, with the aid of AFL. (cherry picked from commit 5b7833cd474a24ec098654dcba8cb9509f3bf2c1) Conflicts: import.c (cherry-picker's note: resolving the conflict involved removing an entire section of the original commit which fixed ECDSA code not present on this branch) changeset: 4619:9c6c638d98d8 user: Simon Tatham <[email protected]> date: Sun Jul 14 10:45:54 2013 +0000 files: import.c ssh.c sshdss.c sshpubk.c sshrsa.c description: Tighten up a lot of casts from unsigned to int which are read by one of the GET_32BIT macros and then used as length fields. Missing bounds checks against zero have been added, and also I've introduced a helper function toint() which casts from unsigned to int in such a way as to avoid C undefined behaviour, since I'm not sure I trust compilers any more to do the obviously sensible thing. [originally from svn r9918] changeset: 4618:3957829f24d3 user: Simon Tatham <[email protected]> date: Mon Jul 08 22:36:04 2013 +0000 files: import.c sshdss.c sshrsa.c description: Add an assortment of extra safety checks. [originally from svn r9896] changeset: 4617:2cddee0bce12 user: Jacob Nevins <[email protected]> date: Wed Dec 07 00:24:45 2005 +0000 files: import.c description: Institutional failure to memset() things pointed at rather than pointers. Things should now be zeroed and memory not leaked. Spotted by Brant Thomsen. [originally from svn r6476] changeset: 4616:24ac78a9c71d user: Simon Tatham <[email protected]> date: Wed Feb 11 13:58:27 2004 +0000 files: import.c description: Jacob's last-minute testing found a couple of trivial bugs in import.c, and my attempts to reproduce them in cmdgen found another one there :-) [originally from svn r3847] changeset: 4615:088d39a73db0 user: Simon Tatham <[email protected]> date: Thu Jan 22 18:52:49 2004 +0000 files: import.c description: Placate some gcc warnings. [originally from svn r3761] changeset: 4614:e4288bad4d93 parent: 1758:108b8924593d user: Simon Tatham <[email protected]> date: Fri Oct 03 21:21:23 2003 +0000 files: import.c description: My ASN.1 decoder returned wrong IDs for anything above 0x1E! Good job it's never had to yet. Ahem. [originally from svn r3479]
author Matt Johnston <matt@ucc.asn.au>
date Tue, 12 Jul 2016 23:00:01 +0800
parents 2bb4c662d1c2
children ad9c40aca3bc
line wrap: on
line source
/*
 * Based on PuTTY's import.c for importing/exporting OpenSSH and SSH.com
 * keyfiles.
 *
 * Modifications copyright 2003 Matt Johnston
 *
 * PuTTY is copyright 1997-2003 Simon Tatham.
 * 
 * Portions copyright Robert de Bath, Joris van Rantwijk, Delian
 * Delchev, Andreas Schultz, Jeroen Massar, Wez Furlong, Nicolas Barry,
 * Justin Bradford, and CORE SDI S.A.
 * 
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation files
 * (the "Software"), to deal in the Software without restriction,
 * including without limitation the rights to use, copy, modify, merge,
 * publish, distribute, sublicense, and/or sell copies of the Software,
 * and to permit persons to whom the Software is furnished to do so,
 * subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT.  IN NO EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE
 * FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
 * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

#include "keyimport.h"
#include "bignum.h"
#include "buffer.h"
#include "dbutil.h"
#include "ecc.h"

static const unsigned char OID_SEC256R1_BLOB[] = {0x2a, 0x86, 0x48, 0xce, 0x3d, 0x03, 0x01, 0x07};
static const unsigned char OID_SEC384R1_BLOB[] = {0x2b, 0x81, 0x04, 0x00, 0x22};
static const unsigned char OID_SEC521R1_BLOB[] = {0x2b, 0x81, 0x04, 0x00, 0x23};

#define PUT_32BIT(cp, value) do { \
  (cp)[3] = (unsigned char)(value); \
  (cp)[2] = (unsigned char)((value) >> 8); \
  (cp)[1] = (unsigned char)((value) >> 16); \
  (cp)[0] = (unsigned char)((value) >> 24); } while (0)

#define GET_32BIT(cp) \
    (((unsigned long)(unsigned char)(cp)[0] << 24) | \
    ((unsigned long)(unsigned char)(cp)[1] << 16) | \
    ((unsigned long)(unsigned char)(cp)[2] << 8) | \
    ((unsigned long)(unsigned char)(cp)[3]))

static int openssh_encrypted(const char *filename);
static sign_key *openssh_read(const char *filename, char *passphrase);
static int openssh_write(const char *filename, sign_key *key,
		  char *passphrase);

static int dropbear_write(const char*filename, sign_key * key);
static sign_key *dropbear_read(const char* filename);

static int toint(unsigned u);

#if 0
static int sshcom_encrypted(const char *filename, char **comment);
static struct ssh2_userkey *sshcom_read(const char *filename, char *passphrase);
static int sshcom_write(const char *filename, struct ssh2_userkey *key,
		 char *passphrase);
#endif

int import_encrypted(const char* filename, int filetype) {

	if (filetype == KEYFILE_OPENSSH) {
	return openssh_encrypted(filename);
#if 0
	} else if (filetype == KEYFILE_SSHCOM) {
		return sshcom_encrypted(filename, NULL);
#endif
    }
    return 0;
}

sign_key *import_read(const char *filename, char *passphrase, int filetype) {

	if (filetype == KEYFILE_OPENSSH) {
	return openssh_read(filename, passphrase);
	} else if (filetype == KEYFILE_DROPBEAR) {
		return dropbear_read(filename);
#if 0
	} else if (filetype == KEYFILE_SSHCOM) {
	return sshcom_read(filename, passphrase);
#endif
	}
    return NULL;
}

int import_write(const char *filename, sign_key *key, char *passphrase,
		int filetype) {

	if (filetype == KEYFILE_OPENSSH) {
	return openssh_write(filename, key, passphrase);
	} else if (filetype == KEYFILE_DROPBEAR) {
		return dropbear_write(filename, key);
#if 0
	} else if (filetype == KEYFILE_SSHCOM) {
	return sshcom_write(filename, key, passphrase);
#endif
	}
    return 0;
}

static sign_key *dropbear_read(const char* filename) {

	buffer * buf = NULL;
	sign_key *ret = NULL;
	enum signkey_type type;

	buf = buf_new(MAX_PRIVKEY_SIZE);
	if (buf_readfile(buf, filename) == DROPBEAR_FAILURE) {
		goto error;
	}

	buf_setpos(buf, 0);
	ret = new_sign_key();

	type = DROPBEAR_SIGNKEY_ANY;
	if (buf_get_priv_key(buf, ret, &type) == DROPBEAR_FAILURE){
		goto error;
	}
	buf_free(buf);

	ret->type = type;

	return ret;

error:
	if (buf) {
		buf_free(buf);
	}
	if (ret) {
		sign_key_free(ret);
	}
	return NULL;
}

/* returns 0 on fail, 1 on success */
static int dropbear_write(const char*filename, sign_key * key) {

	buffer * buf;
	FILE*fp;
	int len;
	int ret;

	buf = buf_new(MAX_PRIVKEY_SIZE);
	buf_put_priv_key(buf, key, key->type);

	fp = fopen(filename, "w");
	if (!fp) {
		ret = 0;
		goto out;
	}

	buf_setpos(buf, 0);
	do {
		len = fwrite(buf_getptr(buf, buf->len - buf->pos),
				1, buf->len - buf->pos, fp);
		buf_incrpos(buf, len);
	} while (len > 0 && buf->len != buf->pos);

	fclose(fp);

	if (buf->pos != buf->len) {
		ret = 0;
	} else {
		ret = 1;
	}
out:
	buf_free(buf);
	return ret;
}


/* ----------------------------------------------------------------------
 * Helper routines. (The base64 ones are defined in sshpubk.c.)
 */

#define isbase64(c) (    ((c) >= 'A' && (c) <= 'Z') || \
                         ((c) >= 'a' && (c) <= 'z') || \
                         ((c) >= '0' && (c) <= '9') || \
                         (c) == '+' || (c) == '/' || (c) == '=' \
                         )

/* cpl has to be less than 100 */
static void base64_encode_fp(FILE * fp, unsigned char *data,
		int datalen, int cpl)
{
	unsigned char out[100];
	int n;
	unsigned long outlen;
	int rawcpl;
	rawcpl = cpl * 3 / 4;
	dropbear_assert((unsigned int)cpl < sizeof(out));

	while (datalen > 0) {
		n = (datalen < rawcpl ? datalen : rawcpl);
		outlen = sizeof(out);
		base64_encode(data, n, out, &outlen);
		data += n;
		datalen -= n;
		fwrite(out, 1, outlen, fp);
		fputc('\n', fp);
	}
}
/*
 * Read an ASN.1/BER identifier and length pair.
 * 
 * Flags are a combination of the #defines listed below.
 * 
 * Returns -1 if unsuccessful; otherwise returns the number of
 * bytes used out of the source data.
 */

/* ASN.1 tag classes. */
#define ASN1_CLASS_UNIVERSAL        (0 << 6)
#define ASN1_CLASS_APPLICATION      (1 << 6)
#define ASN1_CLASS_CONTEXT_SPECIFIC (2 << 6)
#define ASN1_CLASS_PRIVATE          (3 << 6)
#define ASN1_CLASS_MASK             (3 << 6)

/* Primitive versus constructed bit. */
#define ASN1_CONSTRUCTED            (1 << 5)

static int ber_read_id_len(void *source, int sourcelen,
			   int *id, int *length, int *flags)
{
    unsigned char *p = (unsigned char *) source;

    if (sourcelen == 0)
	return -1;

    *flags = (*p & 0xE0);
    if ((*p & 0x1F) == 0x1F) {
	*id = 0;
	while (*p & 0x80) {
	    p++, sourcelen--;
	    if (sourcelen == 0)
		return -1;
	    *id = (*id << 7) | (*p & 0x7F);
	}
	p++, sourcelen--;
    } else {
	*id = *p & 0x1F;
	p++, sourcelen--;
    }

    if (sourcelen == 0)
	return -1;

    if (*p & 0x80) {
        unsigned len;
	int n = *p & 0x7F;
	p++, sourcelen--;
	if (sourcelen < n)
	    return -1;
	len = 0;
	while (n--)
	    len = (len << 8) | (*p++);
	sourcelen -= n;
        *length = toint(len);
    } else {
	*length = *p;
	p++, sourcelen--;
    }

    return p - (unsigned char *) source;
}

/*
 * Write an ASN.1/BER identifier and length pair. Returns the
 * number of bytes consumed. Assumes dest contains enough space.
 * Will avoid writing anything if dest is NULL, but still return
 * amount of space required.
 */
static int ber_write_id_len(void *dest, int id, int length, int flags)
{
    unsigned char *d = (unsigned char *)dest;
    int len = 0;

    if (id <= 30) {
	/*
	 * Identifier is one byte.
	 */
	len++;
	if (d) *d++ = id | flags;
    } else {
	int n;
	/*
	 * Identifier is multiple bytes: the first byte is 11111
	 * plus the flags, and subsequent bytes encode the value of
	 * the identifier, 7 bits at a time, with the top bit of
	 * each byte 1 except the last one which is 0.
	 */
	len++;
	if (d) *d++ = 0x1F | flags;
	for (n = 1; (id >> (7*n)) > 0; n++)
	    continue;		       /* count the bytes */
	while (n--) {
	    len++;
	    if (d) *d++ = (n ? 0x80 : 0) | ((id >> (7*n)) & 0x7F);
	}
    }

    if (length < 128) {
	/*
	 * Length is one byte.
	 */
	len++;
	if (d) *d++ = length;
    } else {
	int n;
	/*
	 * Length is multiple bytes. The first is 0x80 plus the
	 * number of subsequent bytes, and the subsequent bytes
	 * encode the actual length.
	 */
	for (n = 1; (length >> (8*n)) > 0; n++)
	    continue;		       /* count the bytes */
	len++;
	if (d) *d++ = 0x80 | n;
	while (n--) {
	    len++;
	    if (d) *d++ = (length >> (8*n)) & 0xFF;
	}
    }

    return len;
}


/* Simple structure to point to an mp-int within a blob. */
struct mpint_pos { void *start; int bytes; };

/* ----------------------------------------------------------------------
 * Code to read and write OpenSSH private keys.
 */

enum { OSSH_DSA, OSSH_RSA, OSSH_EC };
struct openssh_key {
    int type;
    int encrypted;
    char iv[32];
    unsigned char *keyblob;
	unsigned int keyblob_len, keyblob_size;
};

static struct openssh_key *load_openssh_key(const char *filename)
{
    struct openssh_key *ret;
	FILE *fp = NULL;
    char buffer[256];
	char *errmsg = NULL, *p = NULL;
    int headers_done;
	unsigned long len, outlen;

	ret = (struct openssh_key*)m_malloc(sizeof(struct openssh_key));
    ret->keyblob = NULL;
    ret->keyblob_len = ret->keyblob_size = 0;
    ret->encrypted = 0;
    memset(ret->iv, 0, sizeof(ret->iv));

	if (strlen(filename) == 1 && filename[0] == '-') {
		fp = stdin;
	} else {
		fp = fopen(filename, "r");
	}
    if (!fp) {
	errmsg = "Unable to open key file";
	goto error;
    }
    if (!fgets(buffer, sizeof(buffer), fp) ||
	0 != strncmp(buffer, "-----BEGIN ", 11) ||
	0 != strcmp(buffer+strlen(buffer)-17, "PRIVATE KEY-----\n")) {
	errmsg = "File does not begin with OpenSSH key header";
	goto error;
    }
    if (!strcmp(buffer, "-----BEGIN RSA PRIVATE KEY-----\n"))
	ret->type = OSSH_RSA;
    else if (!strcmp(buffer, "-----BEGIN DSA PRIVATE KEY-----\n"))
	ret->type = OSSH_DSA;
	else if (!strcmp(buffer, "-----BEGIN EC PRIVATE KEY-----\n"))
		ret->type = OSSH_EC;
    else {
	errmsg = "Unrecognised key type";
	goto error;
    }

    headers_done = 0;
    while (1) {
	if (!fgets(buffer, sizeof(buffer), fp)) {
	    errmsg = "Unexpected end of file";
	    goto error;
	}
	if (0 == strncmp(buffer, "-----END ", 9) &&
	    0 == strcmp(buffer+strlen(buffer)-17, "PRIVATE KEY-----\n"))
	    break;		       /* done */
	if ((p = strchr(buffer, ':')) != NULL) {
	    if (headers_done) {
		errmsg = "Header found in body of key data";
		goto error;
	    }
	    *p++ = '\0';
	    while (*p && isspace((unsigned char)*p)) p++;
	    if (!strcmp(buffer, "Proc-Type")) {
		if (p[0] != '4' || p[1] != ',') {
		    errmsg = "Proc-Type is not 4 (only 4 is supported)";
		    goto error;
		}
		p += 2;
		if (!strcmp(p, "ENCRYPTED\n"))
		    ret->encrypted = 1;
	    } else if (!strcmp(buffer, "DEK-Info")) {
		int i, j;

		if (strncmp(p, "DES-EDE3-CBC,", 13)) {
		    errmsg = "Ciphers other than DES-EDE3-CBC not supported";
		    goto error;
		}
		p += 13;
		for (i = 0; i < 8; i++) {
		    if (1 != sscanf(p, "%2x", &j))
			break;
		    ret->iv[i] = j;
		    p += 2;
		}
		if (i < 8) {
		    errmsg = "Expected 16-digit iv in DEK-Info";
		    goto error;
		}
	    }
	} else {
	    headers_done = 1;
			len = strlen(buffer);
			outlen = len*4/3;
			if (ret->keyblob_len + outlen > ret->keyblob_size) {
				ret->keyblob_size = ret->keyblob_len + outlen + 256;
				ret->keyblob = (unsigned char*)m_realloc(ret->keyblob,
						ret->keyblob_size);
			}
			outlen = ret->keyblob_size - ret->keyblob_len;
			if (base64_decode((const unsigned char *)buffer, len,
						ret->keyblob + ret->keyblob_len, &outlen) != CRYPT_OK){
				errmsg = "Error decoding base64";
                        goto error;
                    }
			ret->keyblob_len += outlen;
                }
	}

    if (ret->keyblob_len == 0 || !ret->keyblob) {
	errmsg = "Key body not present";
	goto error;
    }

    if (ret->encrypted && ret->keyblob_len % 8 != 0) {
	errmsg = "Encrypted key blob is not a multiple of cipher block size";
	goto error;
    }

	m_burn(buffer, sizeof(buffer));
    return ret;

    error:
	m_burn(buffer, sizeof(buffer));
    if (ret) {
	if (ret->keyblob) {
			m_burn(ret->keyblob, ret->keyblob_size);
			m_free(ret->keyblob);
        }
		m_free(ret);
	}
	if (fp) {
		fclose(fp);
    }
	if (errmsg) {
		fprintf(stderr, "Error: %s\n", errmsg);
	}
    return NULL;
}

static int openssh_encrypted(const char *filename)
{
    struct openssh_key *key = load_openssh_key(filename);
    int ret;

    if (!key)
	return 0;
    ret = key->encrypted;
	m_burn(key->keyblob, key->keyblob_size);
	m_free(key->keyblob);
	m_free(key);
    return ret;
}

static sign_key *openssh_read(const char *filename, char * UNUSED(passphrase))
{
	struct openssh_key *key;
    unsigned char *p;
    int ret, id, len, flags;
	int i, num_integers = 0;
	sign_key *retval = NULL;
    char *errmsg;
	unsigned char *modptr = NULL;
	int modlen = -9999;
	enum signkey_type type;

	sign_key *retkey;
	buffer * blobbuf = NULL;

	retkey = new_sign_key();

	key = load_openssh_key(filename);

    if (!key)
	return NULL;

    if (key->encrypted) {
		errmsg = "encrypted keys not supported currently";
		goto error;
#if 0
		/* matt TODO */
	/*
	 * Derive encryption key from passphrase and iv/salt:
	 * 
	 *  - let block A equal MD5(passphrase || iv)
	 *  - let block B equal MD5(A || passphrase || iv)
	 *  - block C would be MD5(B || passphrase || iv) and so on
	 *  - encryption key is the first N bytes of A || B
	 */
	struct MD5Context md5c;
	unsigned char keybuf[32];

	MD5Init(&md5c);
	MD5Update(&md5c, (unsigned char *)passphrase, strlen(passphrase));
	MD5Update(&md5c, (unsigned char *)key->iv, 8);
	MD5Final(keybuf, &md5c);

	MD5Init(&md5c);
	MD5Update(&md5c, keybuf, 16);
	MD5Update(&md5c, (unsigned char *)passphrase, strlen(passphrase));
	MD5Update(&md5c, (unsigned char *)key->iv, 8);
	MD5Final(keybuf+16, &md5c);

	/*
	 * Now decrypt the key blob.
	 */
	des3_decrypt_pubkey_ossh(keybuf, (unsigned char *)key->iv,
				 key->keyblob, key->keyblob_len);

        memset(&md5c, 0, sizeof(md5c));
        memset(keybuf, 0, sizeof(keybuf));
#endif 
    }

    /*
     * Now we have a decrypted key blob, which contains an ASN.1
     * encoded private key. We must now untangle the ASN.1.
     *
     * We expect the whole key blob to be formatted as a SEQUENCE
     * (0x30 followed by a length code indicating that the rest of
     * the blob is part of the sequence). Within that SEQUENCE we
     * expect to see a bunch of INTEGERs. What those integers mean
     * depends on the key type:
     *
     *  - For RSA, we expect the integers to be 0, n, e, d, p, q,
     *    dmp1, dmq1, iqmp in that order. (The last three are d mod
     *    (p-1), d mod (q-1), inverse of q mod p respectively.)
     *
     *  - For DSA, we expect them to be 0, p, q, g, y, x in that
     *    order.
     */
    
    p = key->keyblob;

    /* Expect the SEQUENCE header. Take its absence as a failure to decrypt. */
    ret = ber_read_id_len(p, key->keyblob_len, &id, &len, &flags);
    p += ret;
    if (ret < 0 || id != 16 || len < 0 ||
        key->keyblob+key->keyblob_len-p < len) {
		errmsg = "ASN.1 decoding failure - wrong password?";
	goto error;
    }

    /* Expect a load of INTEGERs. */
    if (key->type == OSSH_RSA)
	num_integers = 9;
    else if (key->type == OSSH_DSA)
	num_integers = 6;
	else if (key->type == OSSH_EC)
		num_integers = 1;

    /*
     * Space to create key blob in.
     */
	blobbuf = buf_new(3000);

#ifdef DROPBEAR_DSS
	if (key->type == OSSH_DSA) {
		buf_putstring(blobbuf, "ssh-dss", 7);
		retkey->type = DROPBEAR_SIGNKEY_DSS;
	} 
#endif
#ifdef DROPBEAR_RSA
	if (key->type == OSSH_RSA) {
		buf_putstring(blobbuf, "ssh-rsa", 7);
		retkey->type = DROPBEAR_SIGNKEY_RSA;
	}
#endif

    for (i = 0; i < num_integers; i++) {
	ret = ber_read_id_len(p, key->keyblob+key->keyblob_len-p,
			      &id, &len, &flags);
	p += ret;
	if (ret < 0 || id != 2 || len < 0 ||
	    key->keyblob+key->keyblob_len-p < len) {
	    errmsg = "ASN.1 decoding failure";
	    goto error;
	}

	if (i == 0) {
			/* First integer is a version indicator */
			int expected = -1;
			switch (key->type) {
				case OSSH_RSA:
				case OSSH_DSA:
					expected = 0;
					break;
				case OSSH_EC:
					expected = 1;
					break;
			}
			if (len != 1 || p[0] != expected) {
		errmsg = "Version number mismatch";
		goto error;
	    }
	} else if (key->type == OSSH_RSA) {
	    /*
			 * OpenSSH key order is n, e, d, p, q, dmp1, dmq1, iqmp
			 * but we want e, n, d, p, q
	     */
	    if (i == 1) {
		/* Save the details for after we deal with number 2. */
				modptr = p;
		modlen = len;
			} else if (i >= 2 && i <= 5) {
				buf_putstring(blobbuf, (const char*)p, len);
		if (i == 2) {
					buf_putstring(blobbuf, (const char*)modptr, modlen);
		}
	    }
	} else if (key->type == OSSH_DSA) {
	    /*
			 * OpenSSH key order is p, q, g, y, x,
			 * we want the same.
	     */
			buf_putstring(blobbuf, (const char*)p, len);
	}

	/* Skip past the number. */
	p += len;
    }

#ifdef DROPBEAR_ECDSA
	if (key->type == OSSH_EC) {
		unsigned char* private_key_bytes = NULL;
		int private_key_len = 0;
		unsigned char* public_key_bytes = NULL;
		int public_key_len = 0;
		ecc_key *ecc = NULL;
		const struct dropbear_ecc_curve *curve = NULL;

		/* See SEC1 v2, Appendix C.4 */
		/* OpenSSL (so OpenSSH) seems to include the optional parts. */

		/* privateKey OCTET STRING, */
		ret = ber_read_id_len(p, key->keyblob+key->keyblob_len-p,
							  &id, &len, &flags);
		p += ret;
		/* id==4 for octet string */
		if (ret < 0 || id != 4 ||
			key->keyblob+key->keyblob_len-p < len) {
			errmsg = "ASN.1 decoding failure";
			goto error;
		}
		private_key_bytes = p;
		private_key_len = len;
		p += len;

		/* parameters [0] ECDomainParameters {{ SECGCurveNames }} OPTIONAL, */
		ret = ber_read_id_len(p, key->keyblob+key->keyblob_len-p,
							  &id, &len, &flags);
		p += ret;
		/* id==0 */
		if (ret < 0 || id != 0) {
			errmsg = "ASN.1 decoding failure";
			goto error;
		}

		ret = ber_read_id_len(p, key->keyblob+key->keyblob_len-p,
							  &id, &len, &flags);
		p += ret;
		/* id==6 for object */
		if (ret < 0 || id != 6 ||
			key->keyblob+key->keyblob_len-p < len) {
			errmsg = "ASN.1 decoding failure";
			goto error;
		}

		if (0) {}
#ifdef DROPBEAR_ECC_256
		else if (len == sizeof(OID_SEC256R1_BLOB) 
			&& memcmp(p, OID_SEC256R1_BLOB, len) == 0) {
			retkey->type = DROPBEAR_SIGNKEY_ECDSA_NISTP256;
			curve = &ecc_curve_nistp256;
		} 
#endif
#ifdef DROPBEAR_ECC_384
		else if (len == sizeof(OID_SEC384R1_BLOB)
			&& memcmp(p, OID_SEC384R1_BLOB, len) == 0) {
			retkey->type = DROPBEAR_SIGNKEY_ECDSA_NISTP384;
			curve = &ecc_curve_nistp384;
		} 
#endif
#ifdef DROPBEAR_ECC_521
		else if (len == sizeof(OID_SEC521R1_BLOB)
			&& memcmp(p, OID_SEC521R1_BLOB, len) == 0) {
			retkey->type = DROPBEAR_SIGNKEY_ECDSA_NISTP521;
			curve = &ecc_curve_nistp521;
		} 
#endif
		else {
			errmsg = "Unknown ECC key type";
			goto error;
		}
		p += len;

		/* publicKey [1] BIT STRING OPTIONAL */
		ret = ber_read_id_len(p, key->keyblob+key->keyblob_len-p,
							  &id, &len, &flags);
		p += ret;
		/* id==1 */
		if (ret < 0 || id != 1) {
			errmsg = "ASN.1 decoding failure";
			goto error;
		}

		ret = ber_read_id_len(p, key->keyblob+key->keyblob_len-p,
							  &id, &len, &flags);
		p += ret;
		/* id==3 for bit string */
		if (ret < 0 || id != 3 ||
			key->keyblob+key->keyblob_len-p < len) {
			errmsg = "ASN.1 decoding failure";
			goto error;
		}
		public_key_bytes = p+1;
		public_key_len = len-1;
		p += len;

		buf_putbytes(blobbuf, public_key_bytes, public_key_len);
		ecc = buf_get_ecc_raw_pubkey(blobbuf, curve);
		if (!ecc) {
			errmsg = "Error parsing ECC key";
			goto error;
		}
		m_mp_alloc_init_multi((mp_int**)&ecc->k, NULL);
		if (mp_read_unsigned_bin(ecc->k, private_key_bytes, private_key_len)
			!= MP_OKAY) {
			errmsg = "Error parsing ECC key";
			goto error;
		}

		*signkey_key_ptr(retkey, retkey->type) = ecc;
	}
#endif /* DROPBEAR_ECDSA */

    /*
     * Now put together the actual key. Simplest way to do this is
     * to assemble our own key blobs and feed them to the createkey
     * functions; this is a bit faffy but it does mean we get all
     * the sanity checks for free.
     */
	if (key->type == OSSH_RSA || key->type == OSSH_DSA) {
		buf_setpos(blobbuf, 0);
		type = DROPBEAR_SIGNKEY_ANY;
		if (buf_get_priv_key(blobbuf, retkey, &type)
				!= DROPBEAR_SUCCESS) {
			errmsg = "unable to create key structure";
			sign_key_free(retkey);
			retkey = NULL;
	goto error;
    }
	}

    errmsg = NULL;                     /* no error */
    retval = retkey;

    error:
	if (blobbuf) {
		buf_burn(blobbuf);
		buf_free(blobbuf);
    }
	m_burn(key->keyblob, key->keyblob_size);
	m_free(key->keyblob);
	m_burn(key, sizeof(*key));
	m_free(key);
	if (errmsg) {
		fprintf(stderr, "Error: %s\n", errmsg);
	}
    return retval;
}

static int openssh_write(const char *filename, sign_key *key,
		  char *passphrase)
{
	buffer * keyblob = NULL;
	buffer * extrablob = NULL; /* used for calculated values to write */
	unsigned char *outblob = NULL;
	int outlen = -9999;
    struct mpint_pos numbers[9];
	int nnumbers = -1, pos = 0, len = 0, seqlen, i;
	char *header = NULL, *footer = NULL;
    char zero[1];
    int ret = 0;
    FILE *fp;

#ifdef DROPBEAR_RSA
	mp_int dmp1, dmq1, iqmp, tmpval; /* for rsa */
#endif

	if (
#ifdef DROPBEAR_RSA
			key->type == DROPBEAR_SIGNKEY_RSA ||
#endif
#ifdef DROPBEAR_DSS
			key->type == DROPBEAR_SIGNKEY_DSS ||
#endif
			0)
	{
    /*
     * Fetch the key blobs.
     */
		keyblob = buf_new(3000);
		buf_put_priv_key(keyblob, key, key->type);

		buf_setpos(keyblob, 0);
		/* skip the "ssh-rsa" or "ssh-dss" header */
		buf_incrpos(keyblob, buf_getint(keyblob));

    /*
     * Find the sequence of integers to be encoded into the OpenSSH
     * key blob, and also decide on the header line.
     */
		numbers[0].start = zero; numbers[0].bytes = 1; zero[0] = '\0';

	#ifdef DROPBEAR_RSA
		if (key->type == DROPBEAR_SIGNKEY_RSA) {

			if (key->rsakey->p == NULL || key->rsakey->q == NULL) {
				fprintf(stderr, "Pre-0.33 Dropbear keys cannot be converted to OpenSSH keys.\n");
				goto error;
			}

			/* e */
			numbers[2].bytes = buf_getint(keyblob);
			numbers[2].start = buf_getptr(keyblob, numbers[2].bytes);
			buf_incrpos(keyblob, numbers[2].bytes);

			/* n */
			numbers[1].bytes = buf_getint(keyblob);
			numbers[1].start = buf_getptr(keyblob, numbers[1].bytes);
			buf_incrpos(keyblob, numbers[1].bytes);

			/* d */
			numbers[3].bytes = buf_getint(keyblob);
			numbers[3].start = buf_getptr(keyblob, numbers[3].bytes);
			buf_incrpos(keyblob, numbers[3].bytes);

			/* p */
			numbers[4].bytes = buf_getint(keyblob);
			numbers[4].start = buf_getptr(keyblob, numbers[4].bytes);
			buf_incrpos(keyblob, numbers[4].bytes);
			
			/* q */
			numbers[5].bytes = buf_getint(keyblob);
			numbers[5].start = buf_getptr(keyblob, numbers[5].bytes);
			buf_incrpos(keyblob, numbers[5].bytes);

			/* now calculate some extra parameters: */
			m_mp_init(&tmpval);
			m_mp_init(&dmp1);
			m_mp_init(&dmq1);
			m_mp_init(&iqmp);

			/* dmp1 = d mod (p-1) */
			if (mp_sub_d(key->rsakey->p, 1, &tmpval) != MP_OKAY) {
				fprintf(stderr, "Bignum error for p-1\n");
				goto error;
			}
			if (mp_mod(key->rsakey->d, &tmpval, &dmp1) != MP_OKAY) {
				fprintf(stderr, "Bignum error for dmp1\n");
				goto error;
			}

			/* dmq1 = d mod (q-1) */
			if (mp_sub_d(key->rsakey->q, 1, &tmpval) != MP_OKAY) {
				fprintf(stderr, "Bignum error for q-1\n");
				goto error;
			}
			if (mp_mod(key->rsakey->d, &tmpval, &dmq1) != MP_OKAY) {
				fprintf(stderr, "Bignum error for dmq1\n");
				goto error;
			}

			/* iqmp = (q^-1) mod p */
			if (mp_invmod(key->rsakey->q, key->rsakey->p, &iqmp) != MP_OKAY) {
				fprintf(stderr, "Bignum error for iqmp\n");
				goto error;
			}

			extrablob = buf_new(2000);
			buf_putmpint(extrablob, &dmp1);
			buf_putmpint(extrablob, &dmq1);
			buf_putmpint(extrablob, &iqmp);
			buf_setpos(extrablob, 0);
			mp_clear(&dmp1);
			mp_clear(&dmq1);
			mp_clear(&iqmp);
			mp_clear(&tmpval);
			
			/* dmp1 */
			numbers[6].bytes = buf_getint(extrablob);
			numbers[6].start = buf_getptr(extrablob, numbers[6].bytes);
			buf_incrpos(extrablob, numbers[6].bytes);
			
			/* dmq1 */
			numbers[7].bytes = buf_getint(extrablob);
			numbers[7].start = buf_getptr(extrablob, numbers[7].bytes);
			buf_incrpos(extrablob, numbers[7].bytes);
			
			/* iqmp */
			numbers[8].bytes = buf_getint(extrablob);
			numbers[8].start = buf_getptr(extrablob, numbers[8].bytes);
			buf_incrpos(extrablob, numbers[8].bytes);

        nnumbers = 9;
        header = "-----BEGIN RSA PRIVATE KEY-----\n";
        footer = "-----END RSA PRIVATE KEY-----\n";
		}
	#endif /* DROPBEAR_RSA */

	#ifdef DROPBEAR_DSS
		if (key->type == DROPBEAR_SIGNKEY_DSS) {

			/* p */
			numbers[1].bytes = buf_getint(keyblob);
			numbers[1].start = buf_getptr(keyblob, numbers[1].bytes);
			buf_incrpos(keyblob, numbers[1].bytes);

			/* q */
			numbers[2].bytes = buf_getint(keyblob);
			numbers[2].start = buf_getptr(keyblob, numbers[2].bytes);
			buf_incrpos(keyblob, numbers[2].bytes);

			/* g */
			numbers[3].bytes = buf_getint(keyblob);
			numbers[3].start = buf_getptr(keyblob, numbers[3].bytes);
			buf_incrpos(keyblob, numbers[3].bytes);

			/* y */
			numbers[4].bytes = buf_getint(keyblob);
			numbers[4].start = buf_getptr(keyblob, numbers[4].bytes);
			buf_incrpos(keyblob, numbers[4].bytes);

			/* x */
			numbers[5].bytes = buf_getint(keyblob);
			numbers[5].start = buf_getptr(keyblob, numbers[5].bytes);
			buf_incrpos(keyblob, numbers[5].bytes);

        nnumbers = 6;
        header = "-----BEGIN DSA PRIVATE KEY-----\n";
        footer = "-----END DSA PRIVATE KEY-----\n";
    }
	#endif /* DROPBEAR_DSS */

    /*
     * Now count up the total size of the ASN.1 encoded integers,
     * so as to determine the length of the containing SEQUENCE.
     */
    len = 0;
    for (i = 0; i < nnumbers; i++) {
	len += ber_write_id_len(NULL, 2, numbers[i].bytes, 0);
	len += numbers[i].bytes;
    }
    seqlen = len;
    /* Now add on the SEQUENCE header. */
    len += ber_write_id_len(NULL, 16, seqlen, ASN1_CONSTRUCTED);
    /* Round up to the cipher block size, ensuring we have at least one
     * byte of padding (see below). */
    outlen = len;
    if (passphrase)
	outlen = (outlen+8) &~ 7;

    /*
     * Now we know how big outblob needs to be. Allocate it.
     */
		outblob = (unsigned char*)m_malloc(outlen);

    /*
     * And write the data into it.
     */
    pos = 0;
    pos += ber_write_id_len(outblob+pos, 16, seqlen, ASN1_CONSTRUCTED);
    for (i = 0; i < nnumbers; i++) {
	pos += ber_write_id_len(outblob+pos, 2, numbers[i].bytes, 0);
	memcpy(outblob+pos, numbers[i].start, numbers[i].bytes);
	pos += numbers[i].bytes;
    }
	} /* end RSA and DSS handling */

#ifdef DROPBEAR_ECDSA
	if (key->type == DROPBEAR_SIGNKEY_ECDSA_NISTP256
		|| key->type == DROPBEAR_SIGNKEY_ECDSA_NISTP384
		|| key->type == DROPBEAR_SIGNKEY_ECDSA_NISTP521) {

		/*  SEC1 V2 appendix c.4
		ECPrivateKey ::= SEQUENCE {
			version INTEGER { ecPrivkeyVer1(1) } (ecPrivkeyVer1),
			privateKey OCTET STRING,
			parameters [0] ECDomainParameters {{ SECGCurveNames }} OPTIONAL, 
			publicKey [1] BIT STRING OPTIONAL
		}
		*/
		buffer *seq_buf = buf_new(400);
		ecc_key **eck = (ecc_key**)signkey_key_ptr(key, key->type);
		const long curve_size = (*eck)->dp->size;
		int curve_oid_len = 0;
		const void* curve_oid = NULL;
		unsigned long pubkey_size = 2*curve_size+1;
		int k_size;
		int err = 0;

		/* version. less than 10 bytes */
		buf_incrwritepos(seq_buf,
			ber_write_id_len(buf_getwriteptr(seq_buf, 10), 2, 1, 0));
		buf_putbyte(seq_buf, 1);

		/* privateKey */
		k_size = mp_unsigned_bin_size((*eck)->k);
		dropbear_assert(k_size <= curve_size);
		buf_incrwritepos(seq_buf,
			ber_write_id_len(buf_getwriteptr(seq_buf, 10), 4, k_size, 0));
		mp_to_unsigned_bin((*eck)->k, buf_getwriteptr(seq_buf, k_size));
		buf_incrwritepos(seq_buf, k_size);

		/* SECGCurveNames */
		switch (key->type)
		{
			case DROPBEAR_SIGNKEY_ECDSA_NISTP256:
				curve_oid_len = sizeof(OID_SEC256R1_BLOB);
				curve_oid = OID_SEC256R1_BLOB;
				break;
			case DROPBEAR_SIGNKEY_ECDSA_NISTP384:
				curve_oid_len = sizeof(OID_SEC384R1_BLOB);
				curve_oid = OID_SEC384R1_BLOB;
				break;
			case DROPBEAR_SIGNKEY_ECDSA_NISTP521:
				curve_oid_len = sizeof(OID_SEC521R1_BLOB);
				curve_oid = OID_SEC521R1_BLOB;
				break;
			default:
				dropbear_exit("Internal error");
		}

		buf_incrwritepos(seq_buf,
			ber_write_id_len(buf_getwriteptr(seq_buf, 10), 0, 2+curve_oid_len, 0xa0));
		/* object == 6 */
		buf_incrwritepos(seq_buf,
			ber_write_id_len(buf_getwriteptr(seq_buf, 10), 6, curve_oid_len, 0));
		buf_putbytes(seq_buf, curve_oid, curve_oid_len);

		buf_incrwritepos(seq_buf,
			ber_write_id_len(buf_getwriteptr(seq_buf, 10), 1, 2+1+pubkey_size, 0xa0));
		buf_incrwritepos(seq_buf,
			ber_write_id_len(buf_getwriteptr(seq_buf, 10), 3, 1+pubkey_size, 0));
		buf_putbyte(seq_buf, 0);
		err = ecc_ansi_x963_export(*eck, buf_getwriteptr(seq_buf, pubkey_size), &pubkey_size);
		if (err != CRYPT_OK) {
			dropbear_exit("ECC error");
		}
		buf_incrwritepos(seq_buf, pubkey_size);

		buf_setpos(seq_buf, 0);
			
		outblob = (unsigned char*)m_malloc(1000);

		pos = 0;
		pos += ber_write_id_len(outblob+pos, 16, seq_buf->len, ASN1_CONSTRUCTED);
		memcpy(&outblob[pos], seq_buf->data, seq_buf->len);
		pos += seq_buf->len;
		len = pos;
		outlen = len;

		buf_burn(seq_buf);
		buf_free(seq_buf);
		seq_buf = NULL;

		header = "-----BEGIN EC PRIVATE KEY-----\n";
		footer = "-----END EC PRIVATE KEY-----\n";
	}
#endif

    /*
     * Padding on OpenSSH keys is deterministic. The number of
     * padding bytes is always more than zero, and always at most
     * the cipher block length. The value of each padding byte is
     * equal to the number of padding bytes. So a plaintext that's
     * an exact multiple of the block size will be padded with 08
     * 08 08 08 08 08 08 08 (assuming a 64-bit block cipher); a
     * plaintext one byte less than a multiple of the block size
     * will be padded with just 01.
     * 
     * This enables the OpenSSL key decryption function to strip
     * off the padding algorithmically and return the unpadded
     * plaintext to the next layer: it looks at the final byte, and
     * then expects to find that many bytes at the end of the data
     * with the same value. Those are all removed and the rest is
     * returned.
     */
	dropbear_assert(pos == len);
    while (pos < outlen) {
        outblob[pos++] = outlen - len;
    }

    /*
     * Encrypt the key.
     */
    if (passphrase) {
		fprintf(stderr, "Encrypted keys aren't supported currently\n");
		goto error;
    }

    /*
     * And save it. We'll use Unix line endings just in case it's
     * subsequently transferred in binary mode.
     */
	if (strlen(filename) == 1 && filename[0] == '-') {
		fp = stdout;
	} else {
		fp = fopen(filename, "wb");	  /* ensure Unix line endings */
	}
	if (!fp) {
		fprintf(stderr, "Failed opening output file\n");
	goto error;
	}
    fputs(header, fp);
	base64_encode_fp(fp, outblob, outlen, 64);
    fputs(footer, fp);
    fclose(fp);
    ret = 1;

    error:
    if (outblob) {
        memset(outblob, 0, outlen);
		m_free(outblob);
    }
	if (keyblob) {
		buf_burn(keyblob);
		buf_free(keyblob);
    }
	if (extrablob) {
		buf_burn(extrablob);
		buf_free(extrablob);
    }
    return ret;
}

#if 0
/* XXX TODO ssh.com stuff isn't going yet */

/* ----------------------------------------------------------------------
 * Code to read ssh.com private keys.
 */

/*
 * The format of the base64 blob is largely ssh2-packet-formatted,
 * except that mpints are a bit different: they're more like the
 * old ssh1 mpint. You have a 32-bit bit count N, followed by
 * (N+7)/8 bytes of data.
 * 
 * So. The blob contains:
 * 
 *  - uint32 0x3f6ff9eb       (magic number)
 *  - uint32 size             (total blob size)
 *  - string key-type         (see below)
 *  - string cipher-type      (tells you if key is encrypted)
 *  - string encrypted-blob
 * 
 * (The first size field includes the size field itself and the
 * magic number before it. All other size fields are ordinary ssh2
 * strings, so the size field indicates how much data is to
 * _follow_.)
 * 
 * The encrypted blob, once decrypted, contains a single string
 * which in turn contains the payload. (This allows padding to be
 * added after that string while still making it clear where the
 * real payload ends. Also it probably makes for a reasonable
 * decryption check.)
 * 
 * The payload blob, for an RSA key, contains:
 *  - mpint e
 *  - mpint d
 *  - mpint n  (yes, the public and private stuff is intermixed)
 *  - mpint u  (presumably inverse of p mod q)
 *  - mpint p  (p is the smaller prime)
 *  - mpint q  (q is the larger)
 * 
 * For a DSA key, the payload blob contains:
 *  - uint32 0
 *  - mpint p
 *  - mpint g
 *  - mpint q
 *  - mpint y
 *  - mpint x
 * 
 * Alternatively, if the parameters are `predefined', that
 * (0,p,g,q) sequence can be replaced by a uint32 1 and a string
 * containing some predefined parameter specification. *shudder*,
 * but I doubt we'll encounter this in real life.
 * 
 * The key type strings are ghastly. The RSA key I looked at had a
 * type string of
 * 
 *   `if-modn{sign{rsa-pkcs1-sha1},encrypt{rsa-pkcs1v2-oaep}}'
 * 
 * and the DSA key wasn't much better:
 * 
 *   `dl-modp{sign{dsa-nist-sha1},dh{plain}}'
 * 
 * It isn't clear that these will always be the same. I think it
 * might be wise just to look at the `if-modn{sign{rsa' and
 * `dl-modp{sign{dsa' prefixes.
 * 
 * Finally, the encryption. The cipher-type string appears to be
 * either `none' or `3des-cbc'. Looks as if this is SSH2-style
 * 3des-cbc (i.e. outer cbc rather than inner). The key is created
 * from the passphrase by means of yet another hashing faff:
 * 
 *  - first 16 bytes are MD5(passphrase)
 *  - next 16 bytes are MD5(passphrase || first 16 bytes)
 *  - if there were more, they'd be MD5(passphrase || first 32),
 *    and so on.
 */

#define SSHCOM_MAGIC_NUMBER 0x3f6ff9eb

struct sshcom_key {
    char comment[256];                 /* allowing any length is overkill */
    unsigned char *keyblob;
    int keyblob_len, keyblob_size;
};

static struct sshcom_key *load_sshcom_key(const char *filename)
{
    struct sshcom_key *ret;
    FILE *fp;
    char buffer[256];
    int len;
    char *errmsg, *p;
    int headers_done;
    char base64_bit[4];
    int base64_chars = 0;

    ret = snew(struct sshcom_key);
    ret->comment[0] = '\0';
    ret->keyblob = NULL;
    ret->keyblob_len = ret->keyblob_size = 0;

	fp = fopen(filename, "r");
    if (!fp) {
	errmsg = "Unable to open key file";
	goto error;
    }
    if (!fgets(buffer, sizeof(buffer), fp) ||
	0 != strcmp(buffer, "---- BEGIN SSH2 ENCRYPTED PRIVATE KEY ----\n")) {
	errmsg = "File does not begin with ssh.com key header";
	goto error;
    }

    headers_done = 0;
    while (1) {
	if (!fgets(buffer, sizeof(buffer), fp)) {
	    errmsg = "Unexpected end of file";
	    goto error;
	}
        if (!strcmp(buffer, "---- END SSH2 ENCRYPTED PRIVATE KEY ----\n"))
            break;                     /* done */
	if ((p = strchr(buffer, ':')) != NULL) {
	    if (headers_done) {
		errmsg = "Header found in body of key data";
		goto error;
	    }
	    *p++ = '\0';
	    while (*p && isspace((unsigned char)*p)) p++;
            /*
             * Header lines can end in a trailing backslash for
             * continuation.
             */
            while ((len = strlen(p)) > (int)(sizeof(buffer) - (p-buffer) -1) ||
                   p[len-1] != '\n' || p[len-2] == '\\') {
                if (len > (int)((p-buffer) + sizeof(buffer)-2)) {
                    errmsg = "Header line too long to deal with";
                    goto error;
                }
                if (!fgets(p+len-2, sizeof(buffer)-(p-buffer)-(len-2), fp)) {
                    errmsg = "Unexpected end of file";
                    goto error;
                }
            }
            p[strcspn(p, "\n")] = '\0';
            if (!strcmp(buffer, "Comment")) {
                /* Strip quotes in comment if present. */
                if (p[0] == '"' && p[strlen(p)-1] == '"') {
                    p++;
                    p[strlen(p)-1] = '\0';
                }
                strncpy(ret->comment, p, sizeof(ret->comment));
                ret->comment[sizeof(ret->comment)-1] = '\0';
            }
	} else {
	    headers_done = 1;

	    p = buffer;
	    while (isbase64(*p)) {
                base64_bit[base64_chars++] = *p;
                if (base64_chars == 4) {
                    unsigned char out[3];

                    base64_chars = 0;

                    len = base64_decode_atom(base64_bit, out);

                    if (len <= 0) {
                        errmsg = "Invalid base64 encoding";
                        goto error;
                    }

                    if (ret->keyblob_len + len > ret->keyblob_size) {
                        ret->keyblob_size = ret->keyblob_len + len + 256;
                        ret->keyblob = sresize(ret->keyblob, ret->keyblob_size,
					       unsigned char);
                    }

                    memcpy(ret->keyblob + ret->keyblob_len, out, len);
                    ret->keyblob_len += len;
                }

		p++;
	    }
	}
    }

    if (ret->keyblob_len == 0 || !ret->keyblob) {
	errmsg = "Key body not present";
	goto error;
    }

    return ret;

    error:
    if (ret) {
	if (ret->keyblob) {
            memset(ret->keyblob, 0, ret->keyblob_size);
			m_free(ret->keyblob);
        }
        memset(ret, 0, sizeof(*ret));
		m_free(ret);
    }
    return NULL;
}

int sshcom_encrypted(const char *filename, char **comment)
{
    struct sshcom_key *key = load_sshcom_key(filename);
    int pos, len, answer;

    *comment = NULL;
    if (!key)
        return 0;

    /*
     * Check magic number.
     */
    if (GET_32BIT(key->keyblob) != 0x3f6ff9eb)
        return 0;                      /* key is invalid */

    /*
     * Find the cipher-type string.
     */
    answer = 0;
    pos = 8;
    if (key->keyblob_len < pos+4)
        goto done;                     /* key is far too short */
    len = toint(GET_32BIT(key->keyblob + pos));
    if (len < 0 || len > key->keyblob_len - pos - 4)
        goto done;                     /* key is far too short */
    pos += 4 + len;                    /* skip key type */
    len = toint(GET_32BIT(key->keyblob + pos)); /* find cipher-type length */
    if (len < 0 || len > key->keyblob_len - pos - 4)
        goto done;                     /* cipher type string is incomplete */
    if (len != 4 || 0 != memcmp(key->keyblob + pos + 4, "none", 4))
        answer = 1;

    done:
    *comment = dupstr(key->comment);
    memset(key->keyblob, 0, key->keyblob_size);
	m_free(key->keyblob);
    memset(key, 0, sizeof(*key));
	m_free(key);
    return answer;
}

static int sshcom_read_mpint(void *data, int len, struct mpint_pos *ret)
{
    unsigned bits, bytes;
    unsigned char *d = (unsigned char *) data;

    if (len < 4)
        goto error;
    bits = GET_32BIT(d);

    bytes = (bits + 7) / 8;
    if (len < 4+bytes)
        goto error;

    ret->start = d + 4;
    ret->bytes = bytes;
    return bytes+4;

    error:
    ret->start = NULL;
    ret->bytes = -1;
    return len;                        /* ensure further calls fail as well */
}

static int sshcom_put_mpint(void *target, void *data, int len)
{
    unsigned char *d = (unsigned char *)target;
    unsigned char *i = (unsigned char *)data;
    int bits = len * 8 - 1;

    while (bits > 0) {
	if (*i & (1 << (bits & 7)))
	    break;
	if (!(bits-- & 7))
	    i++, len--;
    }

    PUT_32BIT(d, bits+1);
    memcpy(d+4, i, len);
    return len+4;
}

sign_key *sshcom_read(const char *filename, char *passphrase)
{
    struct sshcom_key *key = load_sshcom_key(filename);
    char *errmsg;
    int pos, len;
    const char prefix_rsa[] = "if-modn{sign{rsa";
    const char prefix_dsa[] = "dl-modp{sign{dsa";
    enum { RSA, DSA } type;
    int encrypted;
    char *ciphertext;
    int cipherlen;
    struct ssh2_userkey *ret = NULL, *retkey;
    const struct ssh_signkey *alg;
    unsigned char *blob = NULL;
    int blobsize = 0, publen, privlen;

    if (!key)
        return NULL;

    /*
     * Check magic number.
     */
    if (GET_32BIT(key->keyblob) != SSHCOM_MAGIC_NUMBER) {
        errmsg = "Key does not begin with magic number";
        goto error;
    }

    /*
     * Determine the key type.
     */
    pos = 8;
    if (key->keyblob_len < pos+4 ||
        (len = GET_32BIT(key->keyblob + pos)) > key->keyblob_len - pos - 4) {
        errmsg = "Key blob does not contain a key type string";
        goto error;
    }
    if (len > sizeof(prefix_rsa) - 1 &&
        !memcmp(key->keyblob+pos+4, prefix_rsa, sizeof(prefix_rsa) - 1)) {
        type = RSA;
    } else if (len > sizeof(prefix_dsa) - 1 &&
        !memcmp(key->keyblob+pos+4, prefix_dsa, sizeof(prefix_dsa) - 1)) {
        type = DSA;
    } else {
        errmsg = "Key is of unknown type";
        goto error;
    }
    pos += 4+len;

    /*
     * Determine the cipher type.
     */
    if (key->keyblob_len < pos+4 ||
        (len = GET_32BIT(key->keyblob + pos)) > key->keyblob_len - pos - 4) {
        errmsg = "Key blob does not contain a cipher type string";
        goto error;
    }
    if (len == 4 && !memcmp(key->keyblob+pos+4, "none", 4))
        encrypted = 0;
    else if (len == 8 && !memcmp(key->keyblob+pos+4, "3des-cbc", 8))
        encrypted = 1;
    else {
        errmsg = "Key encryption is of unknown type";
        goto error;
    }
    pos += 4+len;

    /*
     * Get hold of the encrypted part of the key.
     */
    if (key->keyblob_len < pos+4 ||
        (len = GET_32BIT(key->keyblob + pos)) > key->keyblob_len - pos - 4) {
        errmsg = "Key blob does not contain actual key data";
        goto error;
    }
    ciphertext = (char *)key->keyblob + pos + 4;
    cipherlen = len;
    if (cipherlen == 0) {
        errmsg = "Length of key data is zero";
        goto error;
    }

    /*
     * Decrypt it if necessary.
     */
    if (encrypted) {
	/*
	 * Derive encryption key from passphrase and iv/salt:
	 * 
	 *  - let block A equal MD5(passphrase)
	 *  - let block B equal MD5(passphrase || A)
	 *  - block C would be MD5(passphrase || A || B) and so on
	 *  - encryption key is the first N bytes of A || B
	 */
	struct MD5Context md5c;
	unsigned char keybuf[32], iv[8];

        if (cipherlen % 8 != 0) {
            errmsg = "Encrypted part of key is not a multiple of cipher block"
                " size";
            goto error;
        }

	MD5Init(&md5c);
	MD5Update(&md5c, (unsigned char *)passphrase, strlen(passphrase));
	MD5Final(keybuf, &md5c);

	MD5Init(&md5c);
	MD5Update(&md5c, (unsigned char *)passphrase, strlen(passphrase));
	MD5Update(&md5c, keybuf, 16);
	MD5Final(keybuf+16, &md5c);

	/*
	 * Now decrypt the key blob.
	 */
        memset(iv, 0, sizeof(iv));
	des3_decrypt_pubkey_ossh(keybuf, iv, (unsigned char *)ciphertext,
				 cipherlen);

        memset(&md5c, 0, sizeof(md5c));
        memset(keybuf, 0, sizeof(keybuf));

        /*
         * Hereafter we return WRONG_PASSPHRASE for any parsing
         * error. (But only if we've just tried to decrypt it!
         * Returning WRONG_PASSPHRASE for an unencrypted key is
         * automatic doom.)
         */
        if (encrypted)
            ret = SSH2_WRONG_PASSPHRASE;
    }

    /*
     * Strip away the containing string to get to the real meat.
     */
    len = toint(GET_32BIT(ciphertext));
    if (len < 0 || len > cipherlen-4) {
        errmsg = "containing string was ill-formed";
        goto error;
    }
    ciphertext += 4;
    cipherlen = len;

    /*
     * Now we break down into RSA versus DSA. In either case we'll
     * construct public and private blobs in our own format, and
     * end up feeding them to alg->createkey().
     */
    blobsize = cipherlen + 256;
    blob = snewn(blobsize, unsigned char);
    privlen = 0;
    if (type == RSA) {
        struct mpint_pos n, e, d, u, p, q;
        int pos = 0;
        pos += sshcom_read_mpint(ciphertext+pos, cipherlen-pos, &e);
        pos += sshcom_read_mpint(ciphertext+pos, cipherlen-pos, &d);
        pos += sshcom_read_mpint(ciphertext+pos, cipherlen-pos, &n);
        pos += sshcom_read_mpint(ciphertext+pos, cipherlen-pos, &u);
        pos += sshcom_read_mpint(ciphertext+pos, cipherlen-pos, &p);
        pos += sshcom_read_mpint(ciphertext+pos, cipherlen-pos, &q);
        if (!q.start) {
            errmsg = "key data did not contain six integers";
            goto error;
        }

        alg = &ssh_rsa;
        pos = 0;
        pos += put_string(blob+pos, "ssh-rsa", 7);
        pos += put_mp(blob+pos, e.start, e.bytes);
        pos += put_mp(blob+pos, n.start, n.bytes);
        publen = pos;
        pos += put_string(blob+pos, d.start, d.bytes);
        pos += put_mp(blob+pos, q.start, q.bytes);
        pos += put_mp(blob+pos, p.start, p.bytes);
        pos += put_mp(blob+pos, u.start, u.bytes);
        privlen = pos - publen;
    } else if (type == DSA) {
        struct mpint_pos p, q, g, x, y;
        int pos = 4;
        if (GET_32BIT(ciphertext) != 0) {
            errmsg = "predefined DSA parameters not supported";
            goto error;
        }
        pos += sshcom_read_mpint(ciphertext+pos, cipherlen-pos, &p);
        pos += sshcom_read_mpint(ciphertext+pos, cipherlen-pos, &g);
        pos += sshcom_read_mpint(ciphertext+pos, cipherlen-pos, &q);
        pos += sshcom_read_mpint(ciphertext+pos, cipherlen-pos, &y);
        pos += sshcom_read_mpint(ciphertext+pos, cipherlen-pos, &x);
        if (!x.start) {
            errmsg = "key data did not contain five integers";
            goto error;
        }

        alg = &ssh_dss;
        pos = 0;
        pos += put_string(blob+pos, "ssh-dss", 7);
        pos += put_mp(blob+pos, p.start, p.bytes);
        pos += put_mp(blob+pos, q.start, q.bytes);
        pos += put_mp(blob+pos, g.start, g.bytes);
        pos += put_mp(blob+pos, y.start, y.bytes);
        publen = pos;
        pos += put_mp(blob+pos, x.start, x.bytes);
        privlen = pos - publen;
    } else
	return NULL;

	dropbear_assert(privlen > 0);			   /* should have bombed by now if not */

    retkey = snew(struct ssh2_userkey);
    retkey->alg = alg;
    retkey->data = alg->createkey(blob, publen, blob+publen, privlen);
    if (!retkey->data) {
		m_free(retkey);
	errmsg = "unable to create key data structure";
	goto error;
    }
    retkey->comment = dupstr(key->comment);

    errmsg = NULL; /* no error */
    ret = retkey;

    error:
    if (blob) {
        memset(blob, 0, blobsize);
		m_free(blob);
    }
    memset(key->keyblob, 0, key->keyblob_size);
	m_free(key->keyblob);
    memset(key, 0, sizeof(*key));
	m_free(key);
    return ret;
}

int sshcom_write(const char *filename, sign_key *key,
		 char *passphrase)
{
    unsigned char *pubblob, *privblob;
    int publen, privlen;
    unsigned char *outblob;
    int outlen;
    struct mpint_pos numbers[6];
    int nnumbers, initial_zero, pos, lenpos, i;
    char *type;
    char *ciphertext;
    int cipherlen;
    int ret = 0;
    FILE *fp;

    /*
     * Fetch the key blobs.
     */
    pubblob = key->alg->public_blob(key->data, &publen);
    privblob = key->alg->private_blob(key->data, &privlen);
    outblob = NULL;

    /*
     * Find the sequence of integers to be encoded into the OpenSSH
     * key blob, and also decide on the header line.
     */
    if (key->alg == &ssh_rsa) {
        int pos;
        struct mpint_pos n, e, d, p, q, iqmp;

        pos = 4 + GET_32BIT(pubblob);
        pos += ssh2_read_mpint(pubblob+pos, publen-pos, &e);
        pos += ssh2_read_mpint(pubblob+pos, publen-pos, &n);
        pos = 0;
        pos += ssh2_read_mpint(privblob+pos, privlen-pos, &d);
        pos += ssh2_read_mpint(privblob+pos, privlen-pos, &p);
        pos += ssh2_read_mpint(privblob+pos, privlen-pos, &q);
        pos += ssh2_read_mpint(privblob+pos, privlen-pos, &iqmp);

		dropbear_assert(e.start && iqmp.start); /* can't go wrong */

        numbers[0] = e;
        numbers[1] = d;
        numbers[2] = n;
        numbers[3] = iqmp;
        numbers[4] = q;
        numbers[5] = p;

        nnumbers = 6;
	initial_zero = 0;
	type = "if-modn{sign{rsa-pkcs1-sha1},encrypt{rsa-pkcs1v2-oaep}}";
    } else if (key->alg == &ssh_dss) {
        int pos;
        struct mpint_pos p, q, g, y, x;

        pos = 4 + GET_32BIT(pubblob);
        pos += ssh2_read_mpint(pubblob+pos, publen-pos, &p);
        pos += ssh2_read_mpint(pubblob+pos, publen-pos, &q);
        pos += ssh2_read_mpint(pubblob+pos, publen-pos, &g);
        pos += ssh2_read_mpint(pubblob+pos, publen-pos, &y);
        pos = 0;
        pos += ssh2_read_mpint(privblob+pos, privlen-pos, &x);

		dropbear_assert(y.start && x.start); /* can't go wrong */

        numbers[0] = p;
        numbers[1] = g;
        numbers[2] = q;
        numbers[3] = y;
        numbers[4] = x;

        nnumbers = 5;
	initial_zero = 1;
	type = "dl-modp{sign{dsa-nist-sha1},dh{plain}}";
    } else {
		dropbear_assert(0);					 /* zoinks! */
    }

    /*
     * Total size of key blob will be somewhere under 512 plus
     * combined length of integers. We'll calculate the more
     * precise size as we construct the blob.
     */
    outlen = 512;
    for (i = 0; i < nnumbers; i++)
	outlen += 4 + numbers[i].bytes;
    outblob = snewn(outlen, unsigned char);

    /*
     * Create the unencrypted key blob.
     */
    pos = 0;
    PUT_32BIT(outblob+pos, SSHCOM_MAGIC_NUMBER); pos += 4;
    pos += 4;			       /* length field, fill in later */
    pos += put_string(outblob+pos, type, strlen(type));
    {
	char *ciphertype = passphrase ? "3des-cbc" : "none";
	pos += put_string(outblob+pos, ciphertype, strlen(ciphertype));
    }
    lenpos = pos;		       /* remember this position */
    pos += 4;			       /* encrypted-blob size */
    pos += 4;			       /* encrypted-payload size */
    if (initial_zero) {
	PUT_32BIT(outblob+pos, 0);
	pos += 4;
    }
    for (i = 0; i < nnumbers; i++)
	pos += sshcom_put_mpint(outblob+pos,
				numbers[i].start, numbers[i].bytes);
    /* Now wrap up the encrypted payload. */
    PUT_32BIT(outblob+lenpos+4, pos - (lenpos+8));
    /* Pad encrypted blob to a multiple of cipher block size. */
    if (passphrase) {
	int padding = -(pos - (lenpos+4)) & 7;
	while (padding--)
	    outblob[pos++] = random_byte();
    }
    ciphertext = (char *)outblob+lenpos+4;
    cipherlen = pos - (lenpos+4);
	dropbear_assert(!passphrase || cipherlen % 8 == 0);
    /* Wrap up the encrypted blob string. */
    PUT_32BIT(outblob+lenpos, cipherlen);
    /* And finally fill in the total length field. */
    PUT_32BIT(outblob+4, pos);

	dropbear_assert(pos < outlen);

    /*
     * Encrypt the key.
     */
    if (passphrase) {
	/*
	 * Derive encryption key from passphrase and iv/salt:
	 * 
	 *  - let block A equal MD5(passphrase)
	 *  - let block B equal MD5(passphrase || A)
	 *  - block C would be MD5(passphrase || A || B) and so on
	 *  - encryption key is the first N bytes of A || B
	 */
	struct MD5Context md5c;
	unsigned char keybuf[32], iv[8];

	MD5Init(&md5c);
	MD5Update(&md5c, (unsigned char *)passphrase, strlen(passphrase));
	MD5Final(keybuf, &md5c);

	MD5Init(&md5c);
	MD5Update(&md5c, (unsigned char *)passphrase, strlen(passphrase));
	MD5Update(&md5c, keybuf, 16);
	MD5Final(keybuf+16, &md5c);

	/*
	 * Now decrypt the key blob.
	 */
        memset(iv, 0, sizeof(iv));
	des3_encrypt_pubkey_ossh(keybuf, iv, (unsigned char *)ciphertext,
				 cipherlen);

        memset(&md5c, 0, sizeof(md5c));
        memset(keybuf, 0, sizeof(keybuf));
    }

    /*
     * And save it. We'll use Unix line endings just in case it's
     * subsequently transferred in binary mode.
     */
	fp = fopen(filename, "wb");	  /* ensure Unix line endings */
    if (!fp)
	goto error;
    fputs("---- BEGIN SSH2 ENCRYPTED PRIVATE KEY ----\n", fp);
    fprintf(fp, "Comment: \"");
    /*
     * Comment header is broken with backslash-newline if it goes
     * over 70 chars. Although it's surrounded by quotes, it
     * _doesn't_ escape backslashes or quotes within the string.
     * Don't ask me, I didn't design it.
     */
    {
	int slen = 60;		       /* starts at 60 due to "Comment: " */
	char *c = key->comment;
	while ((int)strlen(c) > slen) {
	    fprintf(fp, "%.*s\\\n", slen, c);
	    c += slen;
	    slen = 70;		       /* allow 70 chars on subsequent lines */
	}
	fprintf(fp, "%s\"\n", c);
    }
	base64_encode_fp(fp, outblob, pos, 70);
    fputs("---- END SSH2 ENCRYPTED PRIVATE KEY ----\n", fp);
    fclose(fp);
    ret = 1;

    error:
    if (outblob) {
        memset(outblob, 0, outlen);
		m_free(outblob);
    }
    if (privblob) {
        memset(privblob, 0, privlen);
		m_free(privblob);
    }
    if (pubblob) {
        memset(pubblob, 0, publen);
		m_free(pubblob);
    }
    return ret;
}
#endif /* ssh.com stuff disabled */

/* From PuTTY misc.c */
static int toint(unsigned u)
{
    /*
     * Convert an unsigned to an int, without running into the
     * undefined behaviour which happens by the strict C standard if
     * the value overflows. You'd hope that sensible compilers would
     * do the sensible thing in response to a cast, but actually I
     * don't trust modern compilers not to do silly things like
     * assuming that _obviously_ you wouldn't have caused an overflow
     * and so they can elide an 'if (i < 0)' test immediately after
     * the cast.
     *
     * Sensible compilers ought of course to optimise this entire
     * function into 'just return the input value'!
     */
    if (u <= (unsigned)INT_MAX)
        return (int)u;
    else if (u >= (unsigned)INT_MIN)   /* wrap in cast _to_ unsigned is OK */
        return INT_MIN + (int)(u - (unsigned)INT_MIN);
    else
        return INT_MIN; /* fallback; should never occur on binary machines */
}