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refactor: remove unused prf hmac impls
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@lrstewart
lrstewart committed Feb 26, 2025
1 parent 24eaea5 commit 5a0917f
Showing 1 changed file with 20 additions and 171 deletions.
191 changes: 20 additions & 171 deletions tls/s2n_prf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -171,175 +171,9 @@ static int s2n_sslv3_prf(struct s2n_connection *conn, struct s2n_blob *secret, s
return 0;
}

#if !defined(OPENSSL_IS_BORINGSSL) && !defined(OPENSSL_IS_AWSLC)
static int s2n_evp_pkey_p_hash_alloc(struct s2n_prf_working_space *ws)
{
POSIX_ENSURE_REF(ws->p_hash.evp_hmac.evp_digest.ctx = S2N_EVP_MD_CTX_NEW());
return 0;
}

static int s2n_evp_pkey_p_hash_digest_init(struct s2n_prf_working_space *ws)
{
POSIX_ENSURE_REF(ws->p_hash.evp_hmac.evp_digest.md);
POSIX_ENSURE_REF(ws->p_hash.evp_hmac.evp_digest.ctx);
POSIX_ENSURE_REF(ws->p_hash.evp_hmac.ctx.evp_pkey);

POSIX_GUARD_OSSL(EVP_DigestSignInit(ws->p_hash.evp_hmac.evp_digest.ctx, NULL, ws->p_hash.evp_hmac.evp_digest.md, NULL, ws->p_hash.evp_hmac.ctx.evp_pkey),
S2N_ERR_P_HASH_INIT_FAILED);

return 0;
}

static int s2n_evp_pkey_p_hash_init(struct s2n_prf_working_space *ws, s2n_hmac_algorithm alg, struct s2n_blob *secret)
{
/* Initialize the message digest */
POSIX_GUARD_RESULT(s2n_hmac_md_from_alg(alg, &ws->p_hash.evp_hmac.evp_digest.md));

/* Initialize the mac key using the provided secret */
POSIX_ENSURE_REF(ws->p_hash.evp_hmac.ctx.evp_pkey = EVP_PKEY_new_mac_key(EVP_PKEY_HMAC, NULL, secret->data, secret->size));

/* Initialize the message digest context with the above message digest and mac key */
return s2n_evp_pkey_p_hash_digest_init(ws);
}

static int s2n_evp_pkey_p_hash_update(struct s2n_prf_working_space *ws, const void *data, uint32_t size)
{
POSIX_GUARD_OSSL(EVP_DigestSignUpdate(ws->p_hash.evp_hmac.evp_digest.ctx, data, (size_t) size), S2N_ERR_P_HASH_UPDATE_FAILED);

return 0;
}

static int s2n_evp_pkey_p_hash_final(struct s2n_prf_working_space *ws, void *digest, uint32_t size)
{
/* EVP_DigestSign API's require size_t data structures */
size_t digest_size = size;

POSIX_GUARD_OSSL(EVP_DigestSignFinal(ws->p_hash.evp_hmac.evp_digest.ctx, (unsigned char *) digest, &digest_size), S2N_ERR_P_HASH_FINAL_FAILED);

return 0;
}

static int s2n_evp_pkey_p_hash_wipe(struct s2n_prf_working_space *ws)
{
POSIX_GUARD_OSSL(S2N_EVP_MD_CTX_RESET(ws->p_hash.evp_hmac.evp_digest.ctx), S2N_ERR_P_HASH_WIPE_FAILED);

return 0;
}

static int s2n_evp_pkey_p_hash_reset(struct s2n_prf_working_space *ws)
{
POSIX_GUARD(s2n_evp_pkey_p_hash_wipe(ws));

/*
* On some cleanup paths s2n_evp_pkey_p_hash_reset can be called before s2n_evp_pkey_p_hash_init so there is nothing
* to reset.
*/
if (ws->p_hash.evp_hmac.ctx.evp_pkey == NULL) {
return S2N_SUCCESS;
}
return s2n_evp_pkey_p_hash_digest_init(ws);
}

static int s2n_evp_pkey_p_hash_cleanup(struct s2n_prf_working_space *ws)
{
/* Prepare the workspace md_ctx for the next p_hash */
POSIX_GUARD(s2n_evp_pkey_p_hash_wipe(ws));

/* Free mac key - PKEYs cannot be reused */
POSIX_ENSURE_REF(ws->p_hash.evp_hmac.ctx.evp_pkey);
EVP_PKEY_free(ws->p_hash.evp_hmac.ctx.evp_pkey);
ws->p_hash.evp_hmac.ctx.evp_pkey = NULL;

return 0;
}

static int s2n_evp_pkey_p_hash_free(struct s2n_prf_working_space *ws)
{
POSIX_ENSURE_REF(ws->p_hash.evp_hmac.evp_digest.ctx);
S2N_EVP_MD_CTX_FREE(ws->p_hash.evp_hmac.evp_digest.ctx);
ws->p_hash.evp_hmac.evp_digest.ctx = NULL;

return 0;
}

static const struct s2n_p_hash_hmac s2n_evp_pkey_p_hash_hmac = {
.alloc = &s2n_evp_pkey_p_hash_alloc,
.init = &s2n_evp_pkey_p_hash_init,
.update = &s2n_evp_pkey_p_hash_update,
.final = &s2n_evp_pkey_p_hash_final,
.reset = &s2n_evp_pkey_p_hash_reset,
.cleanup = &s2n_evp_pkey_p_hash_cleanup,
.free = &s2n_evp_pkey_p_hash_free,
};
#else
static int s2n_evp_hmac_p_hash_alloc(struct s2n_prf_working_space *ws)
{
POSIX_ENSURE_REF(ws->p_hash.evp_hmac.ctx.hmac_ctx = HMAC_CTX_new());
return S2N_SUCCESS;
}

static int s2n_evp_hmac_p_hash_init(struct s2n_prf_working_space *ws, s2n_hmac_algorithm alg, struct s2n_blob *secret)
{
/* Figure out the correct EVP_MD from s2n_hmac_algorithm */
POSIX_GUARD_RESULT(s2n_hmac_md_from_alg(alg, &ws->p_hash.evp_hmac.evp_digest.md));

/* Initialize the mac and digest */
POSIX_GUARD_OSSL(HMAC_Init_ex(ws->p_hash.evp_hmac.ctx.hmac_ctx, secret->data, secret->size, ws->p_hash.evp_hmac.evp_digest.md, NULL), S2N_ERR_P_HASH_INIT_FAILED);
return S2N_SUCCESS;
}

static int s2n_evp_hmac_p_hash_update(struct s2n_prf_working_space *ws, const void *data, uint32_t size)
{
POSIX_GUARD_OSSL(HMAC_Update(ws->p_hash.evp_hmac.ctx.hmac_ctx, data, (size_t) size), S2N_ERR_P_HASH_UPDATE_FAILED);
return S2N_SUCCESS;
}

static int s2n_evp_hmac_p_hash_final(struct s2n_prf_working_space *ws, void *digest, uint32_t size)
{
/* HMAC_Final API's require size_t data structures */
unsigned int digest_size = size;
POSIX_GUARD_OSSL(HMAC_Final(ws->p_hash.evp_hmac.ctx.hmac_ctx, (unsigned char *) digest, &digest_size), S2N_ERR_P_HASH_FINAL_FAILED);
return S2N_SUCCESS;
}

static int s2n_evp_hmac_p_hash_reset(struct s2n_prf_working_space *ws)
{
POSIX_ENSURE_REF(ws);
if (ws->p_hash.evp_hmac.evp_digest.md == NULL) {
return S2N_SUCCESS;
}
POSIX_GUARD_OSSL(HMAC_Init_ex(ws->p_hash.evp_hmac.ctx.hmac_ctx, NULL, 0, ws->p_hash.evp_hmac.evp_digest.md, NULL), S2N_ERR_P_HASH_INIT_FAILED);
return S2N_SUCCESS;
}

static int s2n_evp_hmac_p_hash_cleanup(struct s2n_prf_working_space *ws)
{
/* Prepare the workspace md_ctx for the next p_hash */
HMAC_CTX_reset(ws->p_hash.evp_hmac.ctx.hmac_ctx);
return S2N_SUCCESS;
}

static int s2n_evp_hmac_p_hash_free(struct s2n_prf_working_space *ws)
{
HMAC_CTX_free(ws->p_hash.evp_hmac.ctx.hmac_ctx);
return S2N_SUCCESS;
}

static const struct s2n_p_hash_hmac s2n_evp_hmac_p_hash_hmac = {
.alloc = &s2n_evp_hmac_p_hash_alloc,
.init = &s2n_evp_hmac_p_hash_init,
.update = &s2n_evp_hmac_p_hash_update,
.final = &s2n_evp_hmac_p_hash_final,
.reset = &s2n_evp_hmac_p_hash_reset,
.cleanup = &s2n_evp_hmac_p_hash_cleanup,
.free = &s2n_evp_hmac_p_hash_free,
};
#endif /* !defined(OPENSSL_IS_BORINGSSL) && !defined(OPENSSL_IS_AWSLC) */

static int s2n_hmac_p_hash_new(struct s2n_prf_working_space *ws)
{
POSIX_GUARD(s2n_hmac_new(&ws->p_hash.s2n_hmac));

return s2n_hmac_init(&ws->p_hash.s2n_hmac, S2N_HMAC_NONE, NULL, 0);
}

Expand Down Expand Up @@ -389,13 +223,24 @@ static const struct s2n_p_hash_hmac s2n_internal_p_hash_hmac = {
.free = &s2n_hmac_p_hash_free,
};

/*
* For now, use the internal s2n-tls hmac abstraction.
* However, that is a custom implementation of hmac built on hashes.
* Ideally we should stop using our custom implementation here and switch
* to using a libcrypto implementation. Unfortunately, what each libcrypto
* can support varies a lot for HMACs.
*
* For historical reference, there used to be two other hmac implementations:
* https://github.com/aws/s2n-tls/blob/711ee0df658cd7c44088cf7a1b20a9f3cf5296d6/tls/s2n_prf.c#L174-L337
* - s2n_evp_hmac_p_hash_hmac required the HMAC_CTX_* methods, which are missing
* from openssl-1.0.2.
* - s2n_evp_pkey_p_hash_hmac required the EVP_PKEY_new_mac_key method, which is
* missing from some versions of awslc. EVP_PKEY_new_mac_key can be replaced
* by the EVP_PKEY_new_raw_private_key method, but that is missing from openssl-1.0.2.
*/
const struct s2n_p_hash_hmac *s2n_get_hmac_implementation()
{
#if defined(OPENSSL_IS_BORINGSSL) || defined(OPENSSL_IS_AWSLC)
return s2n_is_in_fips_mode() ? &s2n_evp_hmac_p_hash_hmac : &s2n_internal_p_hash_hmac;
#else
return s2n_is_in_fips_mode() ? &s2n_evp_pkey_p_hash_hmac : &s2n_internal_p_hash_hmac;
#endif
return &s2n_internal_p_hash_hmac;
}

static int s2n_p_hash(struct s2n_prf_working_space *ws, s2n_hmac_algorithm alg, struct s2n_blob *secret, struct s2n_blob *label,
Expand All @@ -405,6 +250,7 @@ static int s2n_p_hash(struct s2n_prf_working_space *ws, s2n_hmac_algorithm alg,
POSIX_GUARD(s2n_hmac_digest_size(alg, &digest_size));

const struct s2n_p_hash_hmac *hmac = s2n_get_hmac_implementation();
POSIX_ENSURE_REF(hmac);

/* First compute hmac(secret + A(0)) */
POSIX_GUARD(hmac->init(ws, alg, secret));
Expand Down Expand Up @@ -471,6 +317,7 @@ S2N_RESULT s2n_prf_new(struct s2n_connection *conn)

/* Allocate the hmac state */
const struct s2n_p_hash_hmac *hmac_impl = s2n_get_hmac_implementation();
RESULT_ENSURE_REF(hmac_impl);
RESULT_GUARD_POSIX(hmac_impl->alloc(conn->prf_space));
return S2N_RESULT_OK;
}
Expand All @@ -481,6 +328,7 @@ S2N_RESULT s2n_prf_wipe(struct s2n_connection *conn)
RESULT_ENSURE_REF(conn->prf_space);

const struct s2n_p_hash_hmac *hmac_impl = s2n_get_hmac_implementation();
RESULT_ENSURE_REF(hmac_impl);
RESULT_GUARD_POSIX(hmac_impl->reset(conn->prf_space));

return S2N_RESULT_OK;
Expand All @@ -494,6 +342,7 @@ S2N_RESULT s2n_prf_free(struct s2n_connection *conn)
}

const struct s2n_p_hash_hmac *hmac_impl = s2n_get_hmac_implementation();
RESULT_ENSURE_REF(hmac_impl);
RESULT_GUARD_POSIX(hmac_impl->free(conn->prf_space));

RESULT_GUARD_POSIX(s2n_free_object((uint8_t **) &conn->prf_space, sizeof(struct s2n_prf_working_space)));
Expand Down

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