--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/keyimport.c	Wed Mar 08 13:23:58 2006 +0000
@@ -0,0 +1,1730 @@
+/*
+ * Based on PuTTY's import.c for importing/exporting OpenSSH and SSH.com
+ * keyfiles.
+ *
+ * The horribleness of the code is probably mine (matt).
+ *
+ * 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"
+
+#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);
+
+#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;
+	int 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);
+
+	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) {
+
+	int keytype = -1;
+	buffer * buf;
+	FILE*fp;
+	int len;
+	int ret;
+
+#ifdef DROPBEAR_RSA
+	if (key->rsakey != NULL) {
+		keytype = DROPBEAR_SIGNKEY_RSA;
+	}
+#endif
+#ifdef DROPBEAR_DSS
+	if (key->dsskey != NULL) {
+		keytype = DROPBEAR_SIGNKEY_DSS;
+	}
+#endif
+
+	buf = buf_new(MAX_PRIVKEY_SIZE);
+	buf_put_priv_key(buf, key, keytype);
+
+	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)
+{
+    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) {
+			*id = (*id << 7) | (*p & 0x7F);
+			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) {
+		int n = *p & 0x7F;
+		p++, sourcelen--;
+		if (sourcelen < n)
+			return -1;
+		*length = 0;
+		while (n--)
+			*length = (*length << 8) | (*p++);
+		sourcelen -= n;
+	} 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 };
+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;
+	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 {
+		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(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;
+	}
+
+	memset(buffer, 0, sizeof(buffer));
+	return ret;
+
+	error:
+	memset(buffer, 0, sizeof(buffer));
+	if (ret) {
+		if (ret->keyblob) {
+			memset(ret->keyblob, 0, ret->keyblob_size);
+			m_free(ret->keyblob);
+		}
+		memset(&ret, 0, sizeof(ret));
+		m_free(ret);
+	}
+	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;
+	memset(key->keyblob, 0, key->keyblob_size);
+	m_free(key->keyblob);
+	memset(&key, 0, sizeof(key));
+	m_free(key);
+	return ret;
+}
+
+static sign_key *openssh_read(const char *filename, char *passphrase)
+{
+	struct openssh_key *key;
+	unsigned char *p;
+	int ret, id, len, flags;
+	int i, num_integers = 0;
+	sign_key *retval = NULL;
+	char *errmsg;
+	char *modptr = NULL;
+	int modlen = -9999;
+	int type;
+
+	sign_key *retkey;
+	buffer * blobbuf = NULL;
+
+	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) {
+		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;
+
+	/*
+	 * Space to create key blob in.
+	 */
+	blobbuf = buf_new(3000);
+
+	if (key->type == OSSH_DSA) {
+		buf_putstring(blobbuf, "ssh-dss", 7);
+	} else if (key->type == OSSH_RSA) {
+		buf_putstring(blobbuf, "ssh-rsa", 7);
+	}
+
+	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 ||
+			key->keyblob+key->keyblob_len-p < len) {
+			errmsg = "ASN.1 decoding failure";
+			goto error;
+		}
+
+		if (i == 0) {
+			/*
+			 * The first integer should be zero always (I think
+			 * this is some sort of version indication).
+			 */
+			if (len != 1 || p[0] != 0) {
+				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 = (char *)p;
+				modlen = len;
+			} else if (i >= 2 && i <= 5) {
+				buf_putstring(blobbuf, p, len);
+				if (i == 2) {
+					buf_putstring(blobbuf, modptr, modlen);
+				}
+			}
+		} else if (key->type == OSSH_DSA) {
+			/*
+			 * OpenSSH key order is p, q, g, y, x,
+			 * we want the same.
+			 */
+			buf_putstring(blobbuf, p, len);
+		}
+
+		/* Skip past the number. */
+		p += len;
+	}
+
+	/*
+	 * 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.
+	 */
+	retkey = new_sign_key();
+	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, len, seqlen, i;
+	char *header = NULL, *footer = NULL;
+	char zero[1];
+	unsigned char iv[8];
+	int ret = 0;
+	FILE *fp;
+	int keytype = -1;
+
+#ifdef DROPBEAR_RSA
+	mp_int dmp1, dmq1, iqmp, tmpval; /* for rsa */
+
+	if (key->rsakey != NULL) {
+		keytype = DROPBEAR_SIGNKEY_RSA;
+	}
+#endif
+#ifdef DROPBEAR_DSS
+	if (key->dsskey != NULL) {
+		keytype = DROPBEAR_SIGNKEY_DSS;
+	}
+#endif
+
+	dropbear_assert(keytype != -1);
+
+	/*
+	 * Fetch the key blobs.
+	 */
+	keyblob = buf_new(3000);
+	buf_put_priv_key(keyblob, key, keytype);
+
+	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 (keytype == 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 (keytype == 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;
+	}
+
+	/*
+	 * 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;
+#if 0
+		/*
+		 * Invent an iv. Then 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];
+
+		for (i = 0; i < 8; i++) iv[i] = random_byte();
+
+		MD5Init(&md5c);
+		MD5Update(&md5c, (unsigned char *)passphrase, strlen(passphrase));
+		MD5Update(&md5c, iv, 8);
+		MD5Final(keybuf, &md5c);
+
+		MD5Init(&md5c);
+		MD5Update(&md5c, keybuf, 16);
+		MD5Update(&md5c, (unsigned char *)passphrase, strlen(passphrase));
+		MD5Update(&md5c, iv, 8);
+		MD5Final(keybuf+16, &md5c);
+
+		/*
+		 * Now encrypt the key blob.
+		 */
+		des3_encrypt_pubkey_ossh(keybuf, iv, outblob, outlen);
+
+		memset(&md5c, 0, sizeof(md5c));
+		memset(keybuf, 0, sizeof(keybuf));
+#endif
+	}
+
+	/*
+	 * 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);
+	if (passphrase) {
+		fprintf(fp, "Proc-Type: 4,ENCRYPTED\nDEK-Info: DES-EDE3-CBC,");
+		for (i = 0; i < 8; i++)
+			fprintf(fp, "%02X", iv[i]);
+		fprintf(fp, "\n\n");
+	}
+	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 */
+	pos += 4 + GET_32BIT(key->keyblob + pos);   /* skip key type */
+	if (key->keyblob_len < pos+4)
+		goto done;					 /* key is far too short */
+	len = GET_32BIT(key->keyblob + pos);   /* find cipher-type length */
+	if (key->keyblob_len < pos+4+len)
+		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)
+{
+	int bits;
+	int 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, 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 = GET_32BIT(ciphertext);
+	if (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;
+	}
+
+	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 */