sshpubk.c

大名鼎鼎的远程登录软件putty的Symbian版源码

/*
 * 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 "putty.h"
#include "ssh.h"
#include "misc.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, int pub_only,
			   char **commentptr, char *passphrase,
			   const char **error)
{
#define BUFSIZE 16384
    unsigned char *buf = snewn(BUFSIZE, unsigned char);
    unsigned char keybuf[16];
    int len;
    int i, j, ciphertype;
    int ret = 0;
    struct MD5Context md5c;
    char *comment;

    *error = NULL;

    /* Slurp the whole file (minus the header) into a buffer. */
    len = fread(buf, 1, BUFSIZE, fp);
    fclose(fp);
    if (len < 0 || len == sizeof(buf)) {
	*error = "error reading file";
	goto end;		       /* file too big or not read */
    }

    i = 0;
    *error = "file format error";

    /*
     * 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, len, key, NULL, 1);
    if (i < 0)
	goto end;		       /* overran */

    if (pub_only) {
	ret = 1;
	goto end;
    }

    /* Next, the comment field. */
    j = GET_32BIT(buf + i);
    i += 4;
    if (len - i < j)
	goto end;
    comment = snewn(j + 1, char);
    if (comment) {
	memcpy(comment, buf + i, j);
	comment[j] = '\0';
    }
    i += j;
    if (commentptr)
	*commentptr = comment;
    if (key)
	key->comment = comment;
    if (!key) {
	ret = ciphertype != 0;
	*error = NULL;
	goto end;
    }

    /*
     * Decrypt remainder of buffer.
     */
    if (ciphertype) {
	MD5Init(&md5c);
	MD5Update(&md5c, (unsigned char *)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]) {
	*error = "wrong passphrase";
	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).
     */
    j = makeprivate(buf + i, len - i, key);
    if (j < 0) goto end;
    i += j;
    j = ssh1_read_bignum(buf + i, len - i, &key->iqmp);
    if (j < 0) goto end;
    i += j;
    j = ssh1_read_bignum(buf + i, len - i, &key->q);
    if (j < 0) goto end;
    i += j;
    j = ssh1_read_bignum(buf + i, len - i, &key->p);
    if (j < 0) goto end;
    i += j;

    if (!rsa_verify(key)) {
	*error = "rsa_verify failed";
	freersakey(key);
	ret = 0;
    } else
	ret = 1;

  end:
    memset(buf, 0, sizeof(buf));       /* burn the evidence */
    sfree(buf);
    return ret;
#undef BUFSIZE
}

int loadrsakey(const Filename *filename, struct RSAKey *key, char *passphrase,
	       const char **errorstr)
{
    FILE *fp;
    char buf[64];
    int ret = 0;
    const char *error = NULL;

    fp = f_open(*filename, "rb");
    if (!fp) {
	error = "can't open file";
	goto end;
    }

    /*
     * 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)) {
	/*
	 * This routine will take care of calling fclose() for us.
	 */
	ret = loadrsakey_main(fp, key, FALSE, NULL, passphrase, &error);
	fp = NULL;
	goto end;
    }

    /*
     * Otherwise, we have nothing. Return empty-handed.
     */
    error = "not an SSH-1 RSA file";

  end:
    if (fp)
	fclose(fp);
    if ((ret != 1) && errorstr)
	*errorstr = error;
    return ret;
}

/*
 * See whether an RSA key is encrypted. Return its comment field as
 * well.
 */
int rsakey_encrypted(const Filename *filename, char **comment)
{
    FILE *fp;
    char buf[64];

    fp = f_open(*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)) {
	const char *dummy;
	/*
	 * This routine will take care of calling fclose() for us.
	 */
	return loadrsakey_main(fp, NULL, FALSE, comment, NULL, &dummy);
    }
    fclose(fp);
    return 0;			       /* wasn't the right kind of file */
}

/*
 * Return a malloc'ed chunk of memory containing the public blob of
 * an RSA key, as given in the agent protocol (modulus bits,
 * exponent, modulus).
 */
int rsakey_pubblob(const Filename *filename, void **blob, int *bloblen,
		   const char **errorstr)
{
    FILE *fp;
    char buf[64];
    struct RSAKey key;
    int ret;
    const char *error = NULL;

    /* Default return if we fail. */
    *blob = NULL;
    *bloblen = 0;
    ret = 0;

    fp = f_open(*filename, "rb");
    if (!fp) {
	error = "can't open file";
	goto end;
    }

    /*
     * 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)) {
	memset(&key, 0, sizeof(key));
	if (loadrsakey_main(fp, &key, TRUE, NULL, NULL, &error)) {
	    *blob = rsa_public_blob(&key, bloblen);
	    freersakey(&key);
	    ret = 1;
	    fp = NULL;
	}
    } else {
	error = "not an SSH-1 RSA file";
    }

  end:
    if (fp)
	fclose(fp);
    if ((ret != 1) && errorstr)
	*errorstr = error;
    return ret;
}

/*
 * Save an RSA key file. Return nonzero on success.
 */
int saversakey(const Filename *filename, struct RSAKey *key, char *passphrase)
{
#define BUFSIZE 16384
    unsigned char *buf = snewn(BUFSIZE, unsigned char);
    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, (unsigned char *)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 = f_open(*filename, "wb");
    if (fp) {
	int ret = (fwrite(buf, 1, p - buf, fp) == (size_t) (p - buf));
	ret = ret && (fclose(fp) == 0);
        sfree(buf);
	return ret;
    } else {
        sfree(buf);
	return 0;
    }
#undef BUFSIZE
}

/* ----------------------------------------------------------------------
 * 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-2: " plus the name of the
 * algorithm ("ssh-dss", "ssh-rsa" etc).
 *
 * 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)
 *
 * And for "ssh-dss", it will be composed of
 *
 *    mpint  x                  (the private key parameter)
 *  [ string hash   20-byte hash of mpints p || q || g   only in old format ]
 * 
 * Finally, there is a line saying "Private-MAC: " plus a hex
 * representation of a HMAC-SHA-1 of:
 *
 *    string  name of algorithm ("ssh-dss", "ssh-rsa")
 *    string  encryption type
 *    string  comment
 *    string  public-blob
 *    string  private-plaintext (the plaintext version of the
 *                               private part, including the final
 *                               padding)
 * 
 * The key to the MAC is itself a SHA-1 hash of:
 * 
 *    data    "putty-private-key-file-mac-key"
 *    data    passphrase
 *
 * (An empty passphrase is used for unencrypted keys.)
 *
 * 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
 *    data    passphrase
 *
 * where the sequence-number increases from zero. As many of these
 * hashes are used as necessary.
 *
 * For backwards compatibility with snapshots between 0.51 and
 * 0.52, we also support the older key file format, which begins
 * with "PuTTY-User-Key-File-1" (version number differs). In this
 * format the Private-MAC: field only covers the private-plaintext
 * field and nothing else (and without the 4-byte string length on
 * the front too). Moreover, for RSA keys the Private-MAC: field
 * can be replaced with a Private-Hash: field which is a plain
 * SHA-1 hash instead of an HMAC. This is not allowable in DSA
 * keys. (Yes, the old format was a mess. Guess why it changed :-)
 */

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 = snewn(size, char);
    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 = sresize(text, size, char);
	}
	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 unsigned 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 = snewn(48 * nlines, unsigned char);
    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;