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/*
* Implementation of HMAC (RFC 2104) for PuTTY, in a general form that
* can wrap any underlying hash function.
*/
#include "ssh.h"
struct hmac {
const ssh_hashalg *hashalg;
ssh_hash *h_outer, *h_inner, *h_live;
uint8_t *digest;
strbuf *text_name;
ssh2_mac mac;
};
struct hmac_extra {
const ssh_hashalg *hashalg_base;
const char *suffix, *annotation;
};
static ssh2_mac *hmac_new(const ssh2_macalg *alg, ssh_cipher *cipher)
{
struct hmac *ctx = snew(struct hmac);
const struct hmac_extra *extra = (const struct hmac_extra *)alg->extra;
ctx->h_outer = ssh_hash_new(extra->hashalg_base);
/* In case that hashalg was a selector vtable, we'll now switch to
* using whatever real one it selected, for all future purposes. */
ctx->hashalg = ssh_hash_alg(ctx->h_outer);
ctx->h_inner = ssh_hash_new(ctx->hashalg);
ctx->h_live = ssh_hash_new(ctx->hashalg);
/*
* HMAC is not well defined as a wrapper on an absolutely general
* hash function; it expects that the function it's wrapping will
* consume data in fixed-size blocks, and it's partially defined
* in terms of that block size. So we insist that the hash we're
* given must have defined a meaningful block size.
*/
assert(ctx->hashalg->blocklen);
ctx->digest = snewn(ctx->hashalg->hlen, uint8_t);
ctx->text_name = strbuf_new();
put_fmt(ctx->text_name, "HMAC-%s%s",
ctx->hashalg->text_basename, extra->suffix);
if (extra->annotation || ctx->hashalg->annotation) {
put_fmt(ctx->text_name, " (");
const char *sep = "";
if (extra->annotation) {
put_fmt(ctx->text_name, "%s%s", sep, extra->annotation);
sep = ", ";
}
if (ctx->hashalg->annotation) {
put_fmt(ctx->text_name, "%s%s", sep, ctx->hashalg->annotation);
sep = ", ";
}
put_fmt(ctx->text_name, ")");
}
ctx->mac.vt = alg;
BinarySink_DELEGATE_INIT(&ctx->mac, ctx->h_live);
return &ctx->mac;
}
static void hmac_free(ssh2_mac *mac)
{
struct hmac *ctx = container_of(mac, struct hmac, mac);
ssh_hash_free(ctx->h_outer);
ssh_hash_free(ctx->h_inner);
ssh_hash_free(ctx->h_live);
smemclr(ctx->digest, ctx->hashalg->hlen);
sfree(ctx->digest);
strbuf_free(ctx->text_name);
smemclr(ctx, sizeof(*ctx));
sfree(ctx);
}
#define PAD_OUTER 0x5C
#define PAD_INNER 0x36
static void hmac_key(ssh2_mac *mac, ptrlen key)
{
struct hmac *ctx = container_of(mac, struct hmac, mac);
const uint8_t *kp;
size_t klen;
strbuf *sb = NULL;
if (key.len > ctx->hashalg->blocklen) {
/*
* RFC 2104 section 2: if the key exceeds the block length of
* the underlying hash, then we start by hashing the key, and
* use that hash as the 'true' key for the HMAC construction.
*/
sb = strbuf_new_nm();
strbuf_append(sb, ctx->hashalg->hlen);
hash_simple(ctx->hashalg, key, sb->u);
kp = sb->u;
klen = sb->len;
} else {
/*
* A short enough key is used as is.
*/
kp = (const uint8_t *)key.ptr;
klen = key.len;
}
ssh_hash_reset(ctx->h_outer);
for (size_t i = 0; i < klen; i++)
put_byte(ctx->h_outer, PAD_OUTER ^ kp[i]);
for (size_t i = klen; i < ctx->hashalg->blocklen; i++)
put_byte(ctx->h_outer, PAD_OUTER);
ssh_hash_reset(ctx->h_inner);
for (size_t i = 0; i < klen; i++)
put_byte(ctx->h_inner, PAD_INNER ^ kp[i]);
for (size_t i = klen; i < ctx->hashalg->blocklen; i++)
put_byte(ctx->h_inner, PAD_INNER);
if (sb)
strbuf_free(sb);
}
static void hmac_start(ssh2_mac *mac)
{
struct hmac *ctx = container_of(mac, struct hmac, mac);
ssh_hash_copyfrom(ctx->h_live, ctx->h_inner);
}
static void hmac_genresult(ssh2_mac *mac, unsigned char *output)
{
struct hmac *ctx = container_of(mac, struct hmac, mac);
ssh_hash *htmp;
/* Leave h_live and h_outer in place, so that the SSH-2 BPP can
* continue regenerating test results from different-length
* prefixes of the packet */
ssh_hash_digest_nondestructive(ctx->h_live, ctx->digest);
htmp = ssh_hash_copy(ctx->h_outer);
put_data(htmp, ctx->digest, ctx->hashalg->hlen);
ssh_hash_final(htmp, ctx->digest);
/*
* Some instances of HMAC truncate the output hash, so instead of
* writing it directly to 'output' we wrote it to our own
* full-length buffer, and now we copy the required amount.
*/
memcpy(output, ctx->digest, mac->vt->len);
smemclr(ctx->digest, ctx->hashalg->hlen);
}
static const char *hmac_text_name(ssh2_mac *mac)
{
struct hmac *ctx = container_of(mac, struct hmac, mac);
return ctx->text_name->s;
}
static const struct hmac_extra ssh_hmac_sha256_extra = { &ssh_sha256, "" };
const ssh2_macalg ssh_hmac_sha256 = {
.new = hmac_new,
.free = hmac_free,
.setkey = hmac_key,
.start = hmac_start,
.genresult = hmac_genresult,
.next_message = nullmac_next_message,
.text_name = hmac_text_name,
.name = "hmac-sha2-256",
.etm_name = "hmac-sha2-256-etm@openssh.com",
.len = 32,
.keylen = 32,
.extra = &ssh_hmac_sha256_extra,
};
static const struct hmac_extra ssh_hmac_md5_extra = { &ssh_md5, "" };
const ssh2_macalg ssh_hmac_md5 = {
.new = hmac_new,
.free = hmac_free,
.setkey = hmac_key,
.start = hmac_start,
.genresult = hmac_genresult,
.next_message = nullmac_next_message,
.text_name = hmac_text_name,
.name = "hmac-md5",
.etm_name = "hmac-md5-etm@openssh.com",
.len = 16,
.keylen = 16,
.extra = &ssh_hmac_md5_extra,
};
static const struct hmac_extra ssh_hmac_sha1_extra = { &ssh_sha1, "" };
const ssh2_macalg ssh_hmac_sha1 = {
.new = hmac_new,
.free = hmac_free,
.setkey = hmac_key,
.start = hmac_start,
.genresult = hmac_genresult,
.next_message = nullmac_next_message,
.text_name = hmac_text_name,
.name = "hmac-sha1",
.etm_name = "hmac-sha1-etm@openssh.com",
.len = 20,
.keylen = 20,
.extra = &ssh_hmac_sha1_extra,
};
static const struct hmac_extra ssh_hmac_sha1_96_extra = { &ssh_sha1, "-96" };
const ssh2_macalg ssh_hmac_sha1_96 = {
.new = hmac_new,
.free = hmac_free,
.setkey = hmac_key,
.start = hmac_start,
.genresult = hmac_genresult,
.next_message = nullmac_next_message,
.text_name = hmac_text_name,
.name = "hmac-sha1-96",
.etm_name = "hmac-sha1-96-etm@openssh.com",
.len = 12,
.keylen = 20,
.extra = &ssh_hmac_sha1_96_extra,
};
static const struct hmac_extra ssh_hmac_sha1_buggy_extra = {
&ssh_sha1, "", "bug-compatible"
};
const ssh2_macalg ssh_hmac_sha1_buggy = {
.new = hmac_new,
.free = hmac_free,
.setkey = hmac_key,
.start = hmac_start,
.genresult = hmac_genresult,
.next_message = nullmac_next_message,
.text_name = hmac_text_name,
.name = "hmac-sha1",
.len = 20,
.keylen = 16,
.extra = &ssh_hmac_sha1_buggy_extra,
};
static const struct hmac_extra ssh_hmac_sha1_96_buggy_extra = {
&ssh_sha1, "-96", "bug-compatible"
};
const ssh2_macalg ssh_hmac_sha1_96_buggy = {
.new = hmac_new,
.free = hmac_free,
.setkey = hmac_key,
.start = hmac_start,
.genresult = hmac_genresult,
.next_message = nullmac_next_message,
.text_name = hmac_text_name,
.name = "hmac-sha1-96",
.len = 12,
.keylen = 16,
.extra = &ssh_hmac_sha1_96_buggy_extra,
};
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