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import.c
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import.c
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/*
* Code for PuTTY to import and export private key files in other
* SSH clients' formats.
*/
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <ctype.h>
#include "putty.h"
#include "ssh.h"
#include "misc.h"
int openssh_encrypted(const Filename *filename);
struct ssh2_userkey *openssh_read(const Filename *filename, char *passphrase,
const char **errmsg_p);
int openssh_write(const Filename *filename, struct ssh2_userkey *key,
char *passphrase);
int sshcom_encrypted(const Filename *filename, char **comment);
struct ssh2_userkey *sshcom_read(const Filename *filename, char *passphrase,
const char **errmsg_p);
int sshcom_write(const Filename *filename, struct ssh2_userkey *key,
char *passphrase);
/*
* Given a key type, determine whether we know how to import it.
*/
int import_possible(int type)
{
if (type == SSH_KEYTYPE_OPENSSH)
return 1;
if (type == SSH_KEYTYPE_SSHCOM)
return 1;
return 0;
}
/*
* Given a key type, determine what native key type
* (SSH_KEYTYPE_SSH1 or SSH_KEYTYPE_SSH2) it will come out as once
* we've imported it.
*/
int import_target_type(int type)
{
/*
* There are no known foreign SSH-1 key formats.
*/
return SSH_KEYTYPE_SSH2;
}
/*
* Determine whether a foreign key is encrypted.
*/
int import_encrypted(const Filename *filename, int type, char **comment)
{
if (type == SSH_KEYTYPE_OPENSSH) {
/* OpenSSH doesn't do key comments */
*comment = dupstr(filename_to_str(filename));
return openssh_encrypted(filename);
}
if (type == SSH_KEYTYPE_SSHCOM) {
return sshcom_encrypted(filename, comment);
}
return 0;
}
/*
* Import an SSH-1 key.
*/
int import_ssh1(const Filename *filename, int type,
struct RSAKey *key, char *passphrase, const char **errmsg_p)
{
return 0;
}
/*
* Import an SSH-2 key.
*/
struct ssh2_userkey *import_ssh2(const Filename *filename, int type,
char *passphrase, const char **errmsg_p)
{
if (type == SSH_KEYTYPE_OPENSSH)
return openssh_read(filename, passphrase, errmsg_p);
if (type == SSH_KEYTYPE_SSHCOM)
return sshcom_read(filename, passphrase, errmsg_p);
return NULL;
}
/*
* Export an SSH-1 key.
*/
int export_ssh1(const Filename *filename, int type, struct RSAKey *key,
char *passphrase)
{
return 0;
}
/*
* Export an SSH-2 key.
*/
int export_ssh2(const Filename *filename, int type,
struct ssh2_userkey *key, char *passphrase)
{
if (type == SSH_KEYTYPE_OPENSSH)
return openssh_write(filename, key, passphrase);
if (type == SSH_KEYTYPE_SSHCOM)
return sshcom_write(filename, key, passphrase);
return 0;
}
/*
* Strip trailing CRs and LFs at the end of a line of text.
*/
void strip_crlf(char *str)
{
char *p = str + strlen(str);
while (p > str && (p[-1] == '\r' || p[-1] == '\n'))
*--p = '\0';
}
/* ----------------------------------------------------------------------
* 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) == '=' \
)
/*
* 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) {
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;
}
static int put_string(void *target, void *data, int len)
{
unsigned char *d = (unsigned char *)target;
PUT_32BIT(d, len);
memcpy(d+4, data, len);
return len+4;
}
static int put_mp(void *target, void *data, int len)
{
unsigned char *d = (unsigned char *)target;
unsigned char *i = (unsigned char *)data;
if (*i & 0x80) {
PUT_32BIT(d, len+1);
d[4] = 0;
memcpy(d+5, data, len);
return len+5;
} else {
PUT_32BIT(d, len);
memcpy(d+4, data, len);
return len+4;
}
}
/* Simple structure to point to an mp-int within a blob. */
struct mpint_pos { void *start; int bytes; };
static int ssh2_read_mpint(void *data, int len, struct mpint_pos *ret)
{
int bytes;
unsigned char *d = (unsigned char *) data;
if (len < 4)
goto error;
bytes = GET_32BIT(d);
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 */
}
/* ----------------------------------------------------------------------
* Code to read and write OpenSSH private keys.
*/
enum { OSSH_DSA, OSSH_RSA };
enum { OSSH_ENC_3DES, OSSH_ENC_AES };
struct openssh_key {
int type;
int encrypted, encryption;
char iv[32];
unsigned char *keyblob;
int keyblob_len, keyblob_size;
};
static struct openssh_key *load_openssh_key(const Filename *filename,
const char **errmsg_p)
{
struct openssh_key *ret;
FILE *fp;
char *line = NULL;
char *errmsg, *p;
int headers_done;
char base64_bit[4];
int base64_chars = 0;
ret = snew(struct openssh_key);
ret->keyblob = NULL;
ret->keyblob_len = ret->keyblob_size = 0;
ret->encrypted = 0;
memset(ret->iv, 0, sizeof(ret->iv));
fp = f_open(*filename, "r", FALSE);
if (!fp) {
errmsg = "unable to open key file";
goto error;
}
if (!(line = fgetline(fp))) {
errmsg = "unexpected end of file";
goto error;
}
strip_crlf(line);
if (0 != strncmp(line, "-----BEGIN ", 11) ||
0 != strcmp(line+strlen(line)-16, "PRIVATE KEY-----")) {
errmsg = "file does not begin with OpenSSH key header";
goto error;
}
if (!strcmp(line, "-----BEGIN RSA PRIVATE KEY-----"))
ret->type = OSSH_RSA;
else if (!strcmp(line, "-----BEGIN DSA PRIVATE KEY-----"))
ret->type = OSSH_DSA;
else {
errmsg = "unrecognised key type";
goto error;
}
memset(line, 0, strlen(line));
sfree(line);
line = NULL;
headers_done = 0;
while (1) {
if (!(line = fgetline(fp))) {
errmsg = "unexpected end of file";
goto error;
}
strip_crlf(line);
if (0 == strncmp(line, "-----END ", 9) &&
0 == strcmp(line+strlen(line)-16, "PRIVATE KEY-----"))
break; /* done */
if ((p = strchr(line, ':')) != 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(line, "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"))
ret->encrypted = 1;
} else if (!strcmp(line, "DEK-Info")) {
int i, j, ivlen;
if (!strncmp(p, "DES-EDE3-CBC,", 13)) {
ret->encryption = OSSH_ENC_3DES;
ivlen = 8;
} else if (!strncmp(p, "AES-128-CBC,", 12)) {
ret->encryption = OSSH_ENC_AES;
ivlen = 16;
} else {
errmsg = "unsupported cipher";
goto error;
}
p = strchr(p, ',') + 1;/* always non-NULL, by above checks */
for (i = 0; i < ivlen; i++) {
if (1 != sscanf(p, "%2x", &j)) {
errmsg = "expected more iv data in DEK-Info";
goto error;
}
ret->iv[i] = j;
p += 2;
}
if (*p) {
errmsg = "more iv data than expected in DEK-Info";
goto error;
}
}
} else {
headers_done = 1;
p = line;
while (isbase64(*p)) {
base64_bit[base64_chars++] = *p;
if (base64_chars == 4) {
unsigned char out[3];
int len;
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;
memset(out, 0, sizeof(out));
}
p++;
}
}
memset(line, 0, strlen(line));
sfree(line);
line = NULL;
}
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(base64_bit, 0, sizeof(base64_bit));
if (errmsg_p) *errmsg_p = NULL;
return ret;
error:
if (line) {
memset(line, 0, strlen(line));
sfree(line);
line = NULL;
}
memset(base64_bit, 0, sizeof(base64_bit));
if (ret) {
if (ret->keyblob) {
memset(ret->keyblob, 0, ret->keyblob_size);
sfree(ret->keyblob);
}
memset(ret, 0, sizeof(*ret));
sfree(ret);
}
if (errmsg_p) *errmsg_p = errmsg;
return NULL;
}
int openssh_encrypted(const Filename *filename)
{
struct openssh_key *key = load_openssh_key(filename, NULL);
int ret;
if (!key)
return 0;
ret = key->encrypted;
memset(key->keyblob, 0, key->keyblob_size);
sfree(key->keyblob);
memset(key, 0, sizeof(*key));
sfree(key);
return ret;
}
struct ssh2_userkey *openssh_read(const Filename *filename, char *passphrase,
const char **errmsg_p)
{
struct openssh_key *key = load_openssh_key(filename, errmsg_p);
struct ssh2_userkey *retkey;
unsigned char *p;
int ret, id, len, flags;
int i, num_integers;
struct ssh2_userkey *retval = NULL;
char *errmsg;
unsigned char *blob;
int blobsize = 0, blobptr, privptr;
char *modptr = NULL;
int modlen = 0;
blob = NULL;
if (!key)
return NULL;
if (key->encrypted) {
/*
* 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
*
* (Note that only 8 bytes of the iv are used for key
* derivation, even when the key is encrypted with AES and
* hence there are 16 bytes available.)
*/
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.
*/
if (key->encryption == OSSH_ENC_3DES)
des3_decrypt_pubkey_ossh(keybuf, (unsigned char *)key->iv,
key->keyblob, key->keyblob_len);
else {
void *ctx;
assert(key->encryption == OSSH_ENC_AES);
ctx = aes_make_context();
aes128_key(ctx, keybuf);
aes_iv(ctx, (unsigned char *)key->iv);
aes_ssh2_decrypt_blk(ctx, key->keyblob, key->keyblob_len);
aes_free_context(ctx);
}
memset(&md5c, 0, sizeof(md5c));
memset(keybuf, 0, sizeof(keybuf));
}
/*
* 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";
retval = SSH2_WRONG_PASSPHRASE;
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
num_integers = 0; /* placate compiler warnings */
/*
* Space to create key blob in.
*/
blobsize = 256+key->keyblob_len;
blob = snewn(blobsize, unsigned char);
PUT_32BIT(blob, 7);
if (key->type == OSSH_DSA)
memcpy(blob+4, "ssh-dss", 7);
else if (key->type == OSSH_RSA)
memcpy(blob+4, "ssh-rsa", 7);
blobptr = 4+7;
privptr = -1;
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";
retval = SSH2_WRONG_PASSPHRASE;
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) {
/*
* Integers 1 and 2 go into the public blob but in the
* opposite order; integers 3, 4, 5 and 8 go into the
* private blob. The other two (6 and 7) are ignored.
*/
if (i == 1) {
/* Save the details for after we deal with number 2. */
modptr = (char *)p;
modlen = len;
} else if (i != 6 && i != 7) {
PUT_32BIT(blob+blobptr, len);
memcpy(blob+blobptr+4, p, len);
blobptr += 4+len;
if (i == 2) {
PUT_32BIT(blob+blobptr, modlen);
memcpy(blob+blobptr+4, modptr, modlen);
blobptr += 4+modlen;
privptr = blobptr;
}
}
} else if (key->type == OSSH_DSA) {
/*
* Integers 1-4 go into the public blob; integer 5 goes
* into the private blob.
*/
PUT_32BIT(blob+blobptr, len);
memcpy(blob+blobptr+4, p, len);
blobptr += 4+len;
if (i == 4)
privptr = blobptr;
}
/* 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.
*/
assert(privptr > 0); /* should have bombed by now if not */
retkey = snew(struct ssh2_userkey);
retkey->alg = (key->type == OSSH_RSA ? &ssh_rsa : &ssh_dss);
retkey->data = retkey->alg->createkey(blob, privptr,
blob+privptr, blobptr-privptr);
if (!retkey->data) {
sfree(retkey);
errmsg = "unable to create key data structure";
goto error;
}
retkey->comment = dupstr("imported-openssh-key");
errmsg = NULL; /* no error */
retval = retkey;
error:
if (blob) {
memset(blob, 0, blobsize);
sfree(blob);
}
memset(key->keyblob, 0, key->keyblob_size);
sfree(key->keyblob);
memset(key, 0, sizeof(*key));
sfree(key);
if (errmsg_p) *errmsg_p = errmsg;
return retval;
}
int openssh_write(const Filename *filename, struct ssh2_userkey *key,
char *passphrase)
{
unsigned char *pubblob, *privblob, *spareblob;
int publen, privlen, sparelen = 0;
unsigned char *outblob;
int outlen;
struct mpint_pos numbers[9];
int nnumbers, pos, len, seqlen, i;
char *header, *footer;
char zero[1];
unsigned char iv[8];
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);
spareblob = 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, dmp1, dmq1;
Bignum bd, bp, bq, bdmp1, bdmq1;
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);
assert(e.start && iqmp.start); /* can't go wrong */
/* We also need d mod (p-1) and d mod (q-1). */
bd = bignum_from_bytes(d.start, d.bytes);
bp = bignum_from_bytes(p.start, p.bytes);
bq = bignum_from_bytes(q.start, q.bytes);
decbn(bp);
decbn(bq);
bdmp1 = bigmod(bd, bp);
bdmq1 = bigmod(bd, bq);
freebn(bd);
freebn(bp);
freebn(bq);
dmp1.bytes = (bignum_bitcount(bdmp1)+8)/8;
dmq1.bytes = (bignum_bitcount(bdmq1)+8)/8;
sparelen = dmp1.bytes + dmq1.bytes;
spareblob = snewn(sparelen, unsigned char);
dmp1.start = spareblob;
dmq1.start = spareblob + dmp1.bytes;
for (i = 0; i < dmp1.bytes; i++)
spareblob[i] = bignum_byte(bdmp1, dmp1.bytes-1 - i);
for (i = 0; i < dmq1.bytes; i++)
spareblob[i+dmp1.bytes] = bignum_byte(bdmq1, dmq1.bytes-1 - i);
freebn(bdmp1);
freebn(bdmq1);
numbers[0].start = zero; numbers[0].bytes = 1; zero[0] = '\0';
numbers[1] = n;
numbers[2] = e;
numbers[3] = d;
numbers[4] = p;
numbers[5] = q;
numbers[6] = dmp1;
numbers[7] = dmq1;
numbers[8] = iqmp;
nnumbers = 9;
header = "-----BEGIN RSA PRIVATE KEY-----\n";
footer = "-----END RSA PRIVATE KEY-----\n";
} 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);
assert(y.start && x.start); /* can't go wrong */
numbers[0].start = zero; numbers[0].bytes = 1; zero[0] = '\0';
numbers[1] = p;
numbers[2] = q;
numbers[3] = g;
numbers[4] = y;
numbers[5] = x;
nnumbers = 6;
header = "-----BEGIN DSA PRIVATE KEY-----\n";
footer = "-----END DSA PRIVATE KEY-----\n";
} else {
assert(0); /* zoinks! */
exit(1); /* XXX: GCC doesn't understand assert() on some systems. */
}
/*
* 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 = snewn(outlen, unsigned char);
/*
* 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.
*/
assert(pos == len);
while (pos < outlen) {
outblob[pos++] = outlen - len;
}
/*
* Encrypt the key.
*
* For the moment, we still encrypt our OpenSSH keys using
* old-style 3DES.
*/
if (passphrase) {
/*
* 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));
}
/*
* And save it. We'll use Unix line endings just in case it's
* subsequently transferred in binary mode.
*/
fp = f_open(*filename, "wb", TRUE); /* ensure Unix line endings */
if (!fp)
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, outblob, outlen, 64);
fputs(footer, fp);
fclose(fp);
ret = 1;
error:
if (outblob) {
memset(outblob, 0, outlen);
sfree(outblob);
}
if (spareblob) {
memset(spareblob, 0, sparelen);
sfree(spareblob);
}
if (privblob) {
memset(privblob, 0, privlen);
sfree(privblob);
}
if (pubblob) {
memset(pubblob, 0, publen);
sfree(pubblob);
}
return ret;
}
/* ----------------------------------------------------------------------
* Code to read ssh.com private keys.
*/
/*
* The format of the base64 blob is largely SSH-2-packet-formatted,
* except that mpints are a bit different: they're more like the
* old SSH-1 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 SSH-2
* 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