/*
 * 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--;
    }

    if (*length < 0) {
    	printf("Negative ASN.1 length\n");
    	return -1;
    }

    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";
	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 || len < 0 ||
			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 || len < 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 || len < 0 ||
			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 || len < 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==3 for bit string */
		if (ret < 0 || id != 3 || len < 0 ||
			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 */
}