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putty
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putty/sshpubk.c

910 строки
23 KiB
C
Исходник Ответственный История

/*
* Generic SSH public-key handling operations. In particular,
* reading of SSH public-key files, and also the generic `sign'
* operation for ssh2 (which checks the type of the key and
* dispatches to the appropriate key-type specific function).
*/
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include "ssh.h"
#define PUT_32BIT(cp, value) do { \
(cp)[3] = (value); \
(cp)[2] = (value) >> 8; \
(cp)[1] = (value) >> 16; \
(cp)[0] = (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]))
#define rsa_signature "SSH PRIVATE KEY FILE FORMAT 1.1\n"
#define BASE64_TOINT(x) ( (x)-'A'<26 ? (x)-'A'+0 :\
(x)-'a'<26 ? (x)-'a'+26 :\
(x)-'0'<10 ? (x)-'0'+52 :\
(x)=='+' ? 62 : \
(x)=='/' ? 63 : 0 )
static int loadrsakey_main(FILE *fp, struct RSAKey *key,
char **commentptr, char *passphrase) {
unsigned char buf[16384];
unsigned char keybuf[16];
int len;
int i, j, ciphertype;
int ret = 0;
struct MD5Context md5c;
char *comment;
/* Slurp the whole file (minus the header) into a buffer. */
len = fread(buf, 1, sizeof(buf), fp);
fclose(fp);
if (len < 0 || len == sizeof(buf))
goto end; /* file too big or not read */
i = 0;
/*
* A zero byte. (The signature includes a terminating NUL.)
*/
if (len-i < 1 || buf[i] != 0)
goto end;
i++;
/* One byte giving encryption type, and one reserved uint32. */
if (len-i < 1)
goto end;
ciphertype = buf[i];
if (ciphertype != 0 && ciphertype != SSH_CIPHER_3DES)
goto end;
i++;
if (len-i < 4)
goto end; /* reserved field not present */
if (buf[i] != 0 || buf[i+1] != 0 || buf[i+2] != 0 || buf[i+3] != 0)
goto end; /* reserved field nonzero, panic! */
i += 4;
/* Now the serious stuff. An ordinary SSH 1 public key. */
i += makekey(buf+i, key, NULL, 1);
if (len-i < 0)
goto end; /* overran */
/* Next, the comment field. */
j = GET_32BIT(buf+i);
i += 4;
if (len-i < j) goto end;
comment = smalloc(j+1);
if (comment) {
memcpy(comment, buf+i, j);
comment[j] = '\0';
}
i += j;
if (commentptr)
*commentptr = comment;
if (key)
key->comment = comment;
if (!key) {
return ciphertype != 0;
}
/*
* Decrypt remainder of buffer.
*/
if (ciphertype) {
MD5Init(&md5c);
MD5Update(&md5c, passphrase, strlen(passphrase));
MD5Final(keybuf, &md5c);
des3_decrypt_pubkey(keybuf, buf+i, (len-i+7)&~7);
memset(keybuf, 0, sizeof(keybuf)); /* burn the evidence */
}
/*
* We are now in the secret part of the key. The first four
* bytes should be of the form a, b, a, b.
*/
if (len-i < 4) goto end;
if (buf[i] != buf[i+2] || buf[i+1] != buf[i+3]) { ret = -1; goto end; }
i += 4;
/*
* After that, we have one further bignum which is our
* decryption exponent, and then the three auxiliary values
* (iqmp, q, p).
*/
i += makeprivate(buf+i, key);
if (len-i < 0) goto end;
i += ssh1_read_bignum(buf+i, &key->iqmp);
if (len-i < 0) goto end;
i += ssh1_read_bignum(buf+i, &key->q);
if (len-i < 0) goto end;
i += ssh1_read_bignum(buf+i, &key->p);
if (len-i < 0) goto end;
if (!rsa_verify(key)) {
freersakey(key);
ret = 0;
} else
ret = 1;
end:
memset(buf, 0, sizeof(buf)); /* burn the evidence */
return ret;
}
int loadrsakey(char *filename, struct RSAKey *key, char *passphrase) {
FILE *fp;
unsigned char buf[64];
fp = fopen(filename, "rb");
if (!fp)
return 0; /* doesn't even exist */
/*
* Read the first line of the file and see if it's a v1 private
* key file.
*/
if (fgets(buf, sizeof(buf), fp) &&
!strcmp(buf, rsa_signature)) {
return loadrsakey_main(fp, key, NULL, passphrase);
}
/*
* Otherwise, we have nothing. Return empty-handed.
*/
fclose(fp);
return 0;
}
/*
* See whether an RSA key is encrypted. Return its comment field as
* well.
*/
int rsakey_encrypted(char *filename, char **comment) {
FILE *fp;
unsigned char buf[64];
fp = fopen(filename, "rb");
if (!fp)
return 0; /* doesn't even exist */
/*
* Read the first line of the file and see if it's a v1 private
* key file.
*/
if (fgets(buf, sizeof(buf), fp) &&
!strcmp(buf, rsa_signature)) {
return loadrsakey_main(fp, NULL, comment, NULL);
}
fclose(fp);
return 0; /* wasn't the right kind of file */
}
/*
* Save an RSA key file. Return nonzero on success.
*/
int saversakey(char *filename, struct RSAKey *key, char *passphrase) {
unsigned char buf[16384];
unsigned char keybuf[16];
struct MD5Context md5c;
unsigned char *p, *estart;
FILE *fp;
/*
* Write the initial signature.
*/
p = buf;
memcpy(p, rsa_signature, sizeof(rsa_signature));
p += sizeof(rsa_signature);
/*
* One byte giving encryption type, and one reserved (zero)
* uint32.
*/
*p++ = (passphrase ? SSH_CIPHER_3DES : 0);
PUT_32BIT(p, 0); p += 4;
/*
* An ordinary SSH 1 public key consists of: a uint32
* containing the bit count, then two bignums containing the
* modulus and exponent respectively.
*/
PUT_32BIT(p, bignum_bitcount(key->modulus)); p += 4;
p += ssh1_write_bignum(p, key->modulus);
p += ssh1_write_bignum(p, key->exponent);
/*
* A string containing the comment field.
*/
if (key->comment) {
PUT_32BIT(p, strlen(key->comment)); p += 4;
memcpy(p, key->comment, strlen(key->comment));
p += strlen(key->comment);
} else {
PUT_32BIT(p, 0); p += 4;
}
/*
* The encrypted portion starts here.
*/
estart = p;
/*
* Two bytes, then the same two bytes repeated.
*/
*p++ = random_byte();
*p++ = random_byte();
p[0] = p[-2]; p[1] = p[-1]; p += 2;
/*
* Four more bignums: the decryption exponent, then iqmp, then
* q, then p.
*/
p += ssh1_write_bignum(p, key->private_exponent);
p += ssh1_write_bignum(p, key->iqmp);
p += ssh1_write_bignum(p, key->q);
p += ssh1_write_bignum(p, key->p);
/*
* Now write zeros until the encrypted portion is a multiple of
* 8 bytes.
*/
while ((p-estart) % 8)
*p++ = '\0';
/*
* Now encrypt the encrypted portion.
*/
if (passphrase) {
MD5Init(&md5c);
MD5Update(&md5c, passphrase, strlen(passphrase));
MD5Final(keybuf, &md5c);
des3_encrypt_pubkey(keybuf, estart, p-estart);
memset(keybuf, 0, sizeof(keybuf)); /* burn the evidence */
}
/*
* Done. Write the result to the file.
*/
fp = fopen(filename, "wb");
if (fp) {
int ret = (fwrite(buf, 1, p-buf, fp) == (size_t)(p-buf));
ret = ret && (fclose(fp) == 0);
return ret;
} else
return 0;
}
/* ----------------------------------------------------------------------
* SSH2 private key load/store functions.
*/
/*
* PuTTY's own format for SSH2 keys is as follows:
*
* The file is text. Lines are terminated by CRLF, although CR-only
* and LF-only are tolerated on input.
*
* The first line says "PuTTY-User-Key-File-1: " plus the name of the
* algorithm ("ssh-dss", "ssh-rsa" etc. Although, of course, this
* being PuTTY, "ssh-dss" is not supported.)
*
* The next line says "Encryption: " plus an encryption type.
* Currently the only supported encryption types are "aes256-cbc"
* and "none".
*
* The next line says "Comment: " plus the comment string.
*
* Next there is a line saying "Public-Lines: " plus a number N.
* The following N lines contain a base64 encoding of the public
* part of the key. This is encoded as the standard SSH2 public key
* blob (with no initial length): so for RSA, for example, it will
* read
*
* string "ssh-rsa"
* mpint exponent
* mpint modulus
*
* Next, there is a line saying "Private-Lines: " plus a number N,
* and then N lines containing the (potentially encrypted) private
* part of the key. For the key type "ssh-rsa", this will be
* composed of
*
* mpint private_exponent
* mpint p (the larger of the two primes)
* mpint q (the smaller prime)
* mpint iqmp (the inverse of q modulo p)
* data padding (to reach a multiple of the cipher block size)
*
* Finally, there is a line saying "Private-Hash: " plus a hex
* representation of a SHA-1 hash of the plaintext version of the
* private part, including the final padding.
*
* If the key is encrypted, the encryption key is derived from the
* passphrase by means of a succession of SHA-1 hashes. Each hash
* is the hash of:
*
* uint32 sequence-number
* string passphrase
*
* where the sequence-number increases from zero. As many of these
* hashes are used as necessary.
*
* NOTE! It is important that all _public_ data can be verified
* with reference to the _private_ data. There exist attacks based
* on modifying the public key but leaving the private section
* intact.
*
* With RSA, this is easy: verify that n = p*q, and also verify
* that e*d == 1 modulo (p-1)(q-1). With DSA (if we were ever to
* support it), we would need to store extra data in the private
* section other than just x.
*/
static int read_header(FILE *fp, char *header) {
int len = 39;
int c;
while (len > 0) {
c = fgetc(fp);
if (c == '\n' || c == '\r' || c == EOF)
return 0; /* failure */
if (c == ':') {
c = fgetc(fp);
if (c != ' ')
return 0;
*header = '\0';
return 1; /* success! */
}
if (len == 0)
return 0; /* failure */
*header++ = c;
len--;
}
return 0; /* failure */
}
static char *read_body(FILE *fp) {
char *text;
int len;
int size;
int c;
size = 128;
text = smalloc(size);
len = 0;
text[len] = '\0';
while (1) {
c = fgetc(fp);
if (c == '\r' || c == '\n') {
c = fgetc(fp);
if (c != '\r' && c != '\n' && c != EOF)
ungetc(c, fp);
return text;
}
if (c == EOF) {
sfree(text);
return NULL;
}
if (len + 1 > size) {
size += 128;
text = srealloc(text, size);
}
text[len++] = c;
text[len] = '\0';
}
}
int base64_decode_atom(char *atom, unsigned char *out) {
int vals[4];
int i, v, len;
unsigned word;
char c;
for (i = 0; i < 4; i++) {
c = atom[i];
if (c >= 'A' && c <= 'Z')
v = c - 'A';
else if (c >= 'a' && c <= 'z')
v = c - 'a' + 26;
else if (c >= '0' && c <= '9')
v = c - '0' + 52;
else if (c == '+')
v = 62;
else if (c == '/')
v = 63;
else if (c == '=')
v = -1;
else
return 0; /* invalid atom */
vals[i] = v;
}
if (vals[0] == -1 || vals[1] == -1)
return 0;
if (vals[2] == -1 && vals[3] != -1)
return 0;
if (vals[3] != -1)
len = 3;
else if (vals[2] != -1)
len = 2;
else
len = 1;
word = ((vals[0] << 18) |
(vals[1] << 12) |
((vals[2] & 0x3F) << 6) |
(vals[3] & 0x3F));
out[0] = (word >> 16) & 0xFF;
if (len > 1)
out[1] = (word >> 8) & 0xFF;
if (len > 2)
out[2] = word & 0xFF;
return len;
}
static char *read_blob(FILE *fp, int nlines, int *bloblen) {
unsigned char *blob;
char *line;
int linelen, len;
int i, j, k;
/* We expect at most 64 base64 characters, ie 48 real bytes, per line. */
blob = smalloc(48 * nlines);
len = 0;
for (i = 0; i < nlines; i++) {
line = read_body(fp);
if (!line) {
sfree(blob);
return NULL;
}
linelen = strlen(line);
if (linelen % 4 != 0 || linelen > 64) {
sfree(blob);
sfree(line);
return NULL;
}
for (j = 0; j < linelen; j += 4) {
k = base64_decode_atom(line+j, blob+len);
if (!k) {
sfree(line);
sfree(blob);
return NULL;
}
len += k;
}
sfree(line);
}
*bloblen = len;
return blob;
}
/*
* Magic error return value for when the passphrase is wrong.
*/
struct ssh2_userkey ssh2_wrong_passphrase = {
NULL, NULL, NULL
};
struct ssh2_userkey *ssh2_load_userkey(char *filename, char *passphrase) {
FILE *fp;
char header[40], *b, *comment, *hash;
const struct ssh_signkey *alg;
struct ssh2_userkey *ret;
int cipher, cipherblk;
unsigned char *public_blob, *private_blob;
int public_blob_len, private_blob_len;
int i;
ret = NULL; /* return NULL for most errors */
comment = hash = NULL;
public_blob = private_blob = NULL;
fp = fopen(filename, "rb");
if (!fp)
goto error;
/* Read the first header line which contains the key type. */
if (!read_header(fp, header) || 0!=strcmp(header, "PuTTY-User-Key-File-1"))
goto error;
if ((b = read_body(fp)) == NULL)
goto error;
/* Select key algorithm structure. Currently only ssh-rsa. */
if (!strcmp(b, "ssh-rsa"))
alg = &ssh_rsa;
else {
sfree(b);
goto error;
}
sfree(b);
/* Read the Encryption header line. */
if (!read_header(fp, header) || 0!=strcmp(header, "Encryption"))
goto error;
if ((b = read_body(fp)) == NULL)
goto error;
if (!strcmp(b, "aes256-cbc")) {
cipher = 1; cipherblk = 16;
} else if (!strcmp(b, "none")) {
cipher = 0; cipherblk = 1;
} else {
sfree(b);
goto error;
}
sfree(b);
/* Read the Comment header line. */
if (!read_header(fp, header) || 0!=strcmp(header, "Comment"))
goto error;
if ((comment = read_body(fp)) == NULL)
goto error;
/* Read the Public-Lines header line and the public blob. */
if (!read_header(fp, header) || 0!=strcmp(header, "Public-Lines"))
goto error;
if ((b = read_body(fp)) == NULL)
goto error;
i = atoi(b);
sfree(b);
if ((public_blob = read_blob(fp, i, &public_blob_len)) == NULL)
goto error;
/* Read the Private-Lines header line and the Private blob. */
if (!read_header(fp, header) || 0!=strcmp(header, "Private-Lines"))
goto error;
if ((b = read_body(fp)) == NULL)
goto error;
i = atoi(b);
sfree(b);
if ((private_blob = read_blob(fp, i, &private_blob_len)) == NULL)
goto error;
/* Read the Private-Hash header line. */
if (!read_header(fp, header) || 0!=strcmp(header, "Private-Hash"))
goto error;
if ((hash = read_body(fp)) == NULL)
goto error;
fclose(fp);
fp = NULL;
/*
* Decrypt the private blob.
*/
if (cipher) {
unsigned char key[40];
SHA_State s;
int passlen;
if (!passphrase)
goto error;
if (private_blob_len % cipherblk)
goto error;
passlen = strlen(passphrase);
SHA_Init(&s);
SHA_Bytes(&s, "\0\0\0\0", 4);
SHA_Bytes(&s, passphrase, passlen);
SHA_Final(&s, key+0);
SHA_Init(&s);
SHA_Bytes(&s, "\0\0\0\1", 4);
SHA_Bytes(&s, passphrase, passlen);
SHA_Final(&s, key+20);
aes256_decrypt_pubkey(key, private_blob, private_blob_len);
}
/*
* Verify the private hash.
*/
{
char realhash[41];
unsigned char binary[20];
SHA_Simple(private_blob, private_blob_len, binary);
for (i = 0; i < 20; i++)
sprintf(realhash+2*i, "%02x", binary[i]);
if (strcmp(hash, realhash)) {
/* An incorrect hash is an unconditional Error if the key is
* unencrypted. Otherwise, it means Wrong Passphrase. */
ret = cipher ? SSH2_WRONG_PASSPHRASE : NULL;
goto error;
}
}
sfree(hash);
/*
* Create and return the key.
*/
ret = smalloc(sizeof(struct ssh2_userkey));
ret->alg = alg;
ret->comment = comment;
ret->data = alg->createkey(public_blob, public_blob_len,
private_blob, private_blob_len);
if (!ret->data) {
sfree(ret->comment);
sfree(ret);
ret = NULL;
}
sfree(public_blob);
sfree(private_blob);
return ret;
/*
* Error processing.
*/
error:
if (fp) fclose(fp);
if (comment) sfree(comment);
if (hash) sfree(hash);
if (public_blob) sfree(public_blob);
if (private_blob) sfree(private_blob);
return ret;
}
char *ssh2_userkey_loadpub(char *filename, char **algorithm, int *pub_blob_len) {
FILE *fp;
char header[40], *b;
const struct ssh_signkey *alg;
unsigned char *public_blob;
int public_blob_len;
int i;
public_blob = NULL;
fp = fopen(filename, "rb");
if (!fp)
goto error;
/* Read the first header line which contains the key type. */
if (!read_header(fp, header) || 0!=strcmp(header, "PuTTY-User-Key-File-1"))
goto error;
if ((b = read_body(fp)) == NULL)
goto error;
/* Select key algorithm structure. Currently only ssh-rsa. */
if (!strcmp(b, "ssh-rsa"))
alg = &ssh_rsa;
else {
sfree(b);
goto error;
}
sfree(b);
/* Read the Encryption header line. */
if (!read_header(fp, header) || 0!=strcmp(header, "Encryption"))
goto error;
if ((b = read_body(fp)) == NULL)
goto error;
sfree(b); /* we don't care */
/* Read the Comment header line. */
if (!read_header(fp, header) || 0!=strcmp(header, "Comment"))
goto error;
if ((b = read_body(fp)) == NULL)
goto error;
sfree(b); /* we don't care */
/* Read the Public-Lines header line and the public blob. */
if (!read_header(fp, header) || 0!=strcmp(header, "Public-Lines"))
goto error;
if ((b = read_body(fp)) == NULL)
goto error;
i = atoi(b);
sfree(b);
if ((public_blob = read_blob(fp, i, &public_blob_len)) == NULL)
goto error;
fclose(fp);
*pub_blob_len = public_blob_len;
*algorithm = alg->name;
return public_blob;
/*
* Error processing.
*/
error:
if (fp) fclose(fp);
if (public_blob) sfree(public_blob);
return NULL;
}
int ssh2_userkey_encrypted(char *filename, char **commentptr) {
FILE *fp;
char header[40], *b, *comment;
int ret;
if (commentptr) *commentptr = NULL;
fp = fopen(filename, "rb");
if (!fp)
return 0;
if (!read_header(fp, header) || 0!=strcmp(header, "PuTTY-User-Key-File-1")) {
fclose(fp); return 0;
}
if ((b = read_body(fp)) == NULL) {
fclose(fp); return 0;
}
sfree(b); /* we don't care about key type here */
/* Read the Encryption header line. */
if (!read_header(fp, header) || 0!=strcmp(header, "Encryption")) {
fclose(fp); return 0;
}
if ((b = read_body(fp)) == NULL) {
fclose(fp); return 0;
}
/* Read the Comment header line. */
if (!read_header(fp, header) || 0!=strcmp(header, "Comment")) {
fclose(fp); sfree(b); return 1;
}
if ((comment = read_body(fp)) == NULL) {
fclose(fp); sfree(b); return 1;
}
if (commentptr) *commentptr = comment;
fclose(fp);
if (!strcmp(b, "aes256-cbc"))
ret = 1;
else
ret = 0;
sfree(b);
return ret;
}
int base64_lines(int datalen) {
/* When encoding, we use 64 chars/line, which equals 48 real chars. */
return (datalen+47) / 48;
}
void base64_encode_atom(unsigned char *data, int n, char *out) {
static const char base64_chars[] =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
unsigned word;
word = data[0] << 16;
if (n > 1)
word |= data[1] << 8;
if (n > 2)
word |= data[2];
out[0] = base64_chars[(word >> 18) & 0x3F];
out[1] = base64_chars[(word >> 12) & 0x3F];
if (n > 1)
out[2] = base64_chars[(word >> 6) & 0x3F];
else
out[2] = '=';
if (n > 2)
out[3] = base64_chars[word & 0x3F];
else
out[3] = '=';
}
void base64_encode(FILE *fp, unsigned char *data, int datalen) {
int linelen = 0;
char out[4];
int n;
while (datalen > 0) {
if (linelen >= 64) {
linelen = 0;
fputc('\n', fp);
}
n = (datalen < 3 ? datalen : 3);
base64_encode_atom(data, n, out);
data += n;
datalen -= n;
fwrite(out, 1, 4, fp);
linelen += 4;
}
fputc('\n', fp);
}
int ssh2_save_userkey(char *filename, struct ssh2_userkey *key, char *passphrase) {
FILE *fp;
unsigned char *pub_blob, *priv_blob, *priv_blob_encrypted;
int pub_blob_len, priv_blob_len, priv_encrypted_len;
int passlen;
int cipherblk;
int i;
char *cipherstr;
unsigned char priv_hash[20];
/*
* Fetch the key component blobs.
*/
pub_blob = key->alg->public_blob(key->data, &pub_blob_len);
priv_blob = key->alg->private_blob(key->data, &priv_blob_len);
if (!pub_blob || !priv_blob) {
sfree(pub_blob);
sfree(priv_blob);
return 0;
}
/*
* Determine encryption details, and encrypt the private blob.
*/
if (passphrase) {
cipherstr = "aes256-cbc";
cipherblk = 16;
} else {
cipherstr = "none";
cipherblk = 1;
}
priv_encrypted_len = priv_blob_len + cipherblk - 1;
priv_encrypted_len -= priv_encrypted_len % cipherblk;
priv_blob_encrypted = smalloc(priv_encrypted_len);
memset(priv_blob_encrypted, 0, priv_encrypted_len);
memcpy(priv_blob_encrypted, priv_blob, priv_blob_len);
/* Create padding based on the SHA hash of the unpadded blob. This prevents
* too easy a known-plaintext attack on the last block. */
SHA_Simple(priv_blob, priv_blob_len, priv_hash);
assert(priv_encrypted_len - priv_blob_len < 20);
memcpy(priv_blob_encrypted + priv_blob_len, priv_hash,
priv_encrypted_len - priv_blob_len);
/* Now create the _real_ private hash. */
SHA_Simple(priv_blob_encrypted, priv_encrypted_len, priv_hash);
if (passphrase) {
char key[40];
SHA_State s;
passlen = strlen(passphrase);
SHA_Init(&s);
SHA_Bytes(&s, "\0\0\0\0", 4);
SHA_Bytes(&s, passphrase, passlen);
SHA_Final(&s, key+0);
SHA_Init(&s);
SHA_Bytes(&s, "\0\0\0\1", 4);
SHA_Bytes(&s, passphrase, passlen);
SHA_Final(&s, key+20);
aes256_encrypt_pubkey(key, priv_blob_encrypted, priv_encrypted_len);
}
fp = fopen(filename, "w");
if (!fp)
return 0;
fprintf(fp, "PuTTY-User-Key-File-1: %s\n", key->alg->name);
fprintf(fp, "Encryption: %s\n", cipherstr);
fprintf(fp, "Comment: %s\n", key->comment);
fprintf(fp, "Public-Lines: %d\n", base64_lines(pub_blob_len));
base64_encode(fp, pub_blob, pub_blob_len);
fprintf(fp, "Private-Lines: %d\n", base64_lines(priv_encrypted_len));
base64_encode(fp, priv_blob_encrypted, priv_encrypted_len);
fprintf(fp, "Private-Hash: ");
for (i = 0; i < 20; i++)
fprintf(fp, "%02x", priv_hash[i]);
fprintf(fp, "\n");
fclose(fp);
return 1;
}
/* ----------------------------------------------------------------------
* A function to determine which version of SSH to try on a private
* key file. Returns 0 on failure, 1 or 2 on success.
*/
int keyfile_version(char *filename) {
FILE *fp;
int i;
fp = fopen(filename, "r");
if (!fp)
return 0;
i = fgetc(fp);
fclose(fp);
if (i == 'S')
return 1; /* "SSH PRIVATE KEY FORMAT" etc */
if (i == 'P') /* "PuTTY-User-Key-File" etc */
return 2;
return 0; /* unrecognised or EOF */
}
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