/*
* Generate a fingerprint string for the key. Compatible with the
* OpenSSH fingerprint code.
*/
char *rsa_ssh1_fingerprint(RSAKey *key)
{
unsigned char digest[16];
strbuf *out;
int i;
/*
* The hash preimage for SSH-1 key fingerprinting consists of the
* modulus and exponent _without_ any preceding length field -
* just the minimum number of bytes to represent each integer,
* stored big-endian, concatenated with no marker at the division
* between them.
*/
ssh_hash *hash = ssh_hash_new(&ssh_md5);
for (size_t i = (mp_get_nbits(key->modulus) + 7) / 8; i-- > 0 ;)
put_byte(hash, mp_get_byte(key->modulus, i));
for (size_t i = (mp_get_nbits(key->exponent) + 7) / 8; i-- > 0 ;)
put_byte(hash, mp_get_byte(key->exponent, i));
ssh_hash_final(hash, digest);
out = strbuf_new();
strbuf_catf(out, "%d ", mp_get_nbits(key->modulus));
for (i = 0; i < 16; i++)
strbuf_catf(out, "%s%02x", i ? ":" : "", digest[i]);
if (key->comment)
strbuf_catf(out, " %s", key->comment);
return strbuf_to_str(out);
}
static mp_int *ecdsa_signing_exponent_from_data(
const struct ec_curve *curve, const struct ecsign_extra *extra,
ptrlen data)
{
/* Hash the data being signed. */
unsigned char hash[MAX_HASH_LEN];
ssh_hash *h = ssh_hash_new(extra->hash);
put_datapl(h, data);
ssh_hash_final(h, hash);
/*
* Take the leftmost b bits of the hash of the signed data (where
* b is the number of bits in order(G)), interpreted big-endian.
*/
mp_int *z = mp_from_bytes_be(make_ptrlen(hash, extra->hash->hlen));
size_t zbits = mp_get_nbits(z);
size_t nbits = mp_get_nbits(curve->w.G_order);
size_t shift = zbits - nbits;
/* Bound the shift count below at 0, using bit twiddling to avoid
* a conditional branch */
shift &= ~-(shift >> (CHAR_BIT * sizeof(size_t) - 1));
mp_int *toret = mp_rshift_safe(z, shift);
mp_free(z);
return toret;
}
static void rsa2_sign(ssh_key *key, ptrlen data,
unsigned flags, BinarySink *bs)
{
RSAKey *rsa = container_of(key, RSAKey, sshk);
unsigned char *bytes;
size_t nbytes;
mp_int *in, *out;
const ssh_hashalg *halg;
const char *sign_alg_name;
halg = rsa2_hash_alg_for_flags(flags, &sign_alg_name);
nbytes = (mp_get_nbits(rsa->modulus) + 7) / 8;
bytes = rsa_pkcs1_signature_string(nbytes, halg, data);
in = mp_from_bytes_be(make_ptrlen(bytes, nbytes));
smemclr(bytes, nbytes);
sfree(bytes);
out = rsa_privkey_op(in, rsa);
mp_free(in);
put_stringz(bs, sign_alg_name);
nbytes = (mp_get_nbits(out) + 7) / 8;
put_uint32(bs, nbytes);
for (size_t i = 0; i < nbytes; i++)
put_byte(bs, mp_get_byte(out, nbytes - 1 - i));
mp_free(out);
}
static EdwardsPoint *eddsa_decode(ptrlen encoded, const struct ec_curve *curve)
{
assert(curve->type == EC_EDWARDS);
assert(curve->fieldBits % 8 == 7);
mp_int *y = mp_from_bytes_le(encoded);
if (mp_get_nbits(y) > curve->fieldBits+1) {
mp_free(y);
return NULL;
}
/* The topmost bit of the encoding isn't part of y, so it stores
* the bottom bit of x. Extract it, and zero that bit in y. */
unsigned desired_x_parity = mp_get_bit(y, curve->fieldBits);
mp_set_bit(y, curve->fieldBits, 0);
EdwardsPoint *P = ecc_edwards_point_new_from_y(
curve->e.ec, y, desired_x_parity);
mp_free(y);
/* A point constructed in this way will always satisfy the curve
* equation, unless ecc.c wasn't able to construct one at all, in
* which case P is now NULL. Either way, return it. */
return P;
}
bool rsa_ssh1_decrypt_pkcs1(mp_int *input, RSAKey *key,
strbuf *outbuf)
{
strbuf *data = strbuf_new_nm();
bool success = false;
BinarySource src[1];
{
mp_int *b = rsa_ssh1_decrypt(input, key);
for (size_t i = (mp_get_nbits(key->modulus) + 7) / 8; i-- > 0 ;) {
put_byte(data, mp_get_byte(b, i));
}
mp_free(b);
}
BinarySource_BARE_INIT(src, data->u, data->len);
/* Check PKCS#1 formatting prefix */
if (get_byte(src) != 0) goto out;
if (get_byte(src) != 2) goto out;
while (1) {
unsigned char byte = get_byte(src);
if (get_err(src)) goto out;
if (byte == 0)
break;
}
/* Everything else is the payload */
success = true;
put_data(outbuf, get_ptr(src), get_avail(src));
out:
strbuf_free(data);
return success;
}
void BinarySource_get_rsa_ssh1_pub(
BinarySource *src, RSAKey *rsa, RsaSsh1Order order)
{
unsigned bits;
mp_int *e, *m;
bits = get_uint32(src);
if (order == RSA_SSH1_EXPONENT_FIRST) {
e = get_mp_ssh1(src);
m = get_mp_ssh1(src);
} else {
m = get_mp_ssh1(src);
e = get_mp_ssh1(src);
}
if (rsa) {
rsa->bits = bits;
rsa->exponent = e;
rsa->modulus = m;
rsa->bytes = (mp_get_nbits(m) + 7) / 8;
} else {
mp_free(e);
mp_free(m);
}
}
static void initialise_common(
struct ec_curve *curve, EllipticCurveType type, mp_int *p)
{
curve->type = type;
curve->p = mp_copy(p);
curve->fieldBits = mp_get_nbits(p);
curve->fieldBytes = (curve->fieldBits + 7) / 8;
}
static void BinarySink_put_mp_le_unsigned(BinarySink *bs, mp_int *x)
{
size_t bytes = (mp_get_nbits(x) + 7) / 8;
put_uint32(bs, bytes);
for (size_t i = 0; i < bytes; ++i)
put_byte(bs, mp_get_byte(x, i));
}
void rsa_ssh1_public_blob(BinarySink *bs, RSAKey *key,
RsaSsh1Order order)
{
put_uint32(bs, mp_get_nbits(key->modulus));
if (order == RSA_SSH1_EXPONENT_FIRST) {
put_mp_ssh1(bs, key->exponent);
put_mp_ssh1(bs, key->modulus);
} else {
put_mp_ssh1(bs, key->modulus);
put_mp_ssh1(bs, key->exponent);
}
}
char *rsa2_invalid(ssh_key *key, unsigned flags)
{
RSAKey *rsa = container_of(key, RSAKey, sshk);
size_t bits = mp_get_nbits(rsa->modulus), nbytes = (bits + 7) / 8;
const char *sign_alg_name;
const ssh_hashalg *halg = rsa2_hash_alg_for_flags(flags, &sign_alg_name);
if (nbytes < rsa_pkcs1_length_of_fixed_parts(halg)) {
return dupprintf(
"%zu-bit RSA key is too short to generate %s signatures",
bits, sign_alg_name);
}
return NULL;
}
static int rsa2_pubkey_bits(const ssh_keyalg *self, ptrlen pub)
{
ssh_key *sshk;
RSAKey *rsa;
int ret;
sshk = rsa2_new_pub(self, pub);
if (!sshk)
return -1;
rsa = container_of(sshk, RSAKey, sshk);
ret = mp_get_nbits(rsa->modulus);
rsa2_freekey(&rsa->sshk);
return ret;
}
static bool rsa2_verify(ssh_key *key, ptrlen sig, ptrlen data)
{
RSAKey *rsa = container_of(key, RSAKey, sshk);
BinarySource src[1];
ptrlen type, in_pl;
mp_int *in, *out;
/* If we need to support variable flags on verify, this is where they go */
const ssh_hashalg *halg = rsa2_hash_alg_for_flags(0, NULL);
/* Start by making sure the key is even long enough to encode a
* signature. If not, everything fails to verify. */
size_t nbytes = (mp_get_nbits(rsa->modulus) + 7) / 8;
if (nbytes < rsa_pkcs1_length_of_fixed_parts(halg))
return false;
BinarySource_BARE_INIT_PL(src, sig);
type = get_string(src);
/*
* RFC 4253 section 6.6: the signature integer in an ssh-rsa
* signature is 'without lengths or padding'. That is, we _don't_
* expect the usual leading zero byte if the topmost bit of the
* first byte is set. (However, because of the possibility of
* BUG_SSH2_RSA_PADDING at the other end, we tolerate it if it's
* there.) So we can't use get_mp_ssh2, which enforces that
* leading-byte scheme; instead we use get_string and
* mp_from_bytes_be, which will tolerate anything.
*/
in_pl = get_string(src);
if (get_err(src) || !ptrlen_eq_string(type, "ssh-rsa"))
return false;
in = mp_from_bytes_be(in_pl);
out = mp_modpow(in, rsa->exponent, rsa->modulus);
mp_free(in);
unsigned diff = 0;
unsigned char *bytes = rsa_pkcs1_signature_string(nbytes, halg, data);
for (size_t i = 0; i < nbytes; i++)
diff |= bytes[nbytes-1 - i] ^ mp_get_byte(out, i);
smemclr(bytes, nbytes);
sfree(bytes);
mp_free(out);
return diff == 0;
}
mp_int *ssh_rsakex_decrypt(
RSAKey *rsa, const ssh_hashalg *h, ptrlen ciphertext)
{
mp_int *b1, *b2;
int outlen, i;
unsigned char *out;
unsigned char labelhash[64];
ssh_hash *hash;
BinarySource src[1];
const int HLEN = h->hlen;
/*
* Decryption side of the RSA key exchange operation.
*/
/* The length of the encrypted data should be exactly the length
* in octets of the RSA modulus.. */
outlen = (7 + mp_get_nbits(rsa->modulus)) / 8;
if (ciphertext.len != outlen)
return NULL;
/* Do the RSA decryption, and extract the result into a byte array. */
b1 = mp_from_bytes_be(ciphertext);
b2 = rsa_privkey_op(b1, rsa);
out = snewn(outlen, unsigned char);
for (i = 0; i < outlen; i++)
out[i] = mp_get_byte(b2, outlen-1-i);
mp_free(b1);
mp_free(b2);
/* Do the OAEP masking operations, in the reverse order from encryption */
oaep_mask(h, out+HLEN+1, outlen-HLEN-1, out+1, HLEN);
oaep_mask(h, out+1, HLEN, out+HLEN+1, outlen-HLEN-1);
/* Check the leading byte is zero. */
if (out[0] != 0) {
sfree(out);
return NULL;
}
/* Check the label hash at position 1+HLEN */
assert(HLEN <= lenof(labelhash));
hash = ssh_hash_new(h);
ssh_hash_final(hash, labelhash);
if (memcmp(out + HLEN + 1, labelhash, HLEN)) {
sfree(out);
return NULL;
}
/* Expect zero bytes followed by a 1 byte */
for (i = 1 + 2 * HLEN; i < outlen; i++) {
if (out[i] == 1) {
i++; /* skip over the 1 byte */
break;
} else if (out[i] != 1) {
sfree(out);
return NULL;
}
}
/* And what's left is the input message data, which should be
* encoded as an ordinary SSH-2 mpint. */
BinarySource_BARE_INIT(src, out + i, outlen - i);
b1 = get_mp_ssh2(src);
sfree(out);
if (get_err(src) || get_avail(src) != 0) {
mp_free(b1);
return NULL;
}
/* Success! */
return b1;
}
strbuf *ssh_rsakex_encrypt(RSAKey *rsa, const ssh_hashalg *h, ptrlen in)
{
mp_int *b1, *b2;
int k, i;
char *p;
const int HLEN = h->hlen;
/*
* Here we encrypt using RSAES-OAEP. Essentially this means:
*
* - we have a SHA-based `mask generation function' which
* creates a pseudo-random stream of mask data
* deterministically from an input chunk of data.
*
* - we have a random chunk of data called a seed.
*
* - we use the seed to generate a mask which we XOR with our
* plaintext.
*
* - then we use _the masked plaintext_ to generate a mask
* which we XOR with the seed.
*
* - then we concatenate the masked seed and the masked
* plaintext, and RSA-encrypt that lot.
*
* The result is that the data input to the encryption function
* is random-looking and (hopefully) contains no exploitable
* structure such as PKCS1-v1_5 does.
*
* For a precise specification, see RFC 3447, section 7.1.1.
* Some of the variable names below are derived from that, so
* it'd probably help to read it anyway.
*/
/* k denotes the length in octets of the RSA modulus. */
k = (7 + mp_get_nbits(rsa->modulus)) / 8;
/* The length of the input data must be at most k - 2hLen - 2. */
assert(in.len > 0 && in.len <= k - 2*HLEN - 2);
/* The length of the output data wants to be precisely k. */
strbuf *toret = strbuf_new_nm();
int outlen = k;
unsigned char *out = strbuf_append(toret, outlen);
/*
* Now perform EME-OAEP encoding. First set up all the unmasked
* output data.
*/
/* Leading byte zero. */
out[0] = 0;
/* At position 1, the seed: HLEN bytes of random data. */
random_read(out + 1, HLEN);
/* At position 1+HLEN, the data block DB, consisting of: */
/* The hash of the label (we only support an empty label here) */
{
ssh_hash *s = ssh_hash_new(h);
ssh_hash_final(s, out + HLEN + 1);
}
/* A bunch of zero octets */
memset(out + 2*HLEN + 1, 0, outlen - (2*HLEN + 1));
/* A single 1 octet, followed by the input message data. */
out[outlen - in.len - 1] = 1;
memcpy(out + outlen - in.len, in.ptr, in.len);
/*
* Now use the seed data to mask the block DB.
*/
oaep_mask(h, out+1, HLEN, out+HLEN+1, outlen-HLEN-1);
/*
* And now use the masked DB to mask the seed itself.
*/
oaep_mask(h, out+HLEN+1, outlen-HLEN-1, out+1, HLEN);
/*
* Now `out' contains precisely the data we want to
* RSA-encrypt.
*/
b1 = mp_from_bytes_be(make_ptrlen(out, outlen));
b2 = mp_modpow(b1, rsa->exponent, rsa->modulus);
p = (char *)out;
for (i = outlen; i--;) {
*p++ = mp_get_byte(b2, i);
}
mp_free(b1);
mp_free(b2);
/*
* And we're done.
*/
return toret;
}
int ssh_rsakex_klen(RSAKey *rsa)
{
return mp_get_nbits(rsa->modulus);
}
