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refactor: remove unused prf hmac impls (#5148)
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@lrstewart
lrstewart authored Feb 28, 2025
1 parent 5479708 commit 3b16449
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Showing 5 changed files with 19 additions and 211 deletions.
8 changes: 0 additions & 8 deletions crypto/s2n_evp.h
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Original file line number Diff line number Diff line change
Expand Up @@ -26,14 +26,6 @@ struct s2n_evp_digest {
EVP_MD_CTX *ctx;
};

struct s2n_evp_hmac_state {
struct s2n_evp_digest evp_digest;
union {
HMAC_CTX *hmac_ctx;
EVP_PKEY *evp_pkey;
} ctx;
};

/* Define API's that change based on the OpenSSL Major Version. */
#if S2N_OPENSSL_VERSION_AT_LEAST(1, 1, 0) && !defined(LIBRESSL_VERSION_NUMBER)
#define S2N_EVP_MD_CTX_NEW() (EVP_MD_CTX_new())
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10 changes: 0 additions & 10 deletions tests/cbmc/include/cbmc_proof/make_common_datastructures.h
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Original file line number Diff line number Diff line change
Expand Up @@ -197,16 +197,6 @@ void cbmc_populate_s2n_evp_digest(struct s2n_evp_digest *evp_digest);
*/
struct s2n_evp_digest* cbmc_allocate_s2n_evp_digest();

/*
* Populates the fields of a pre-allocated s2n_evp_digest for CBMC proofs.
*/
void cbmc_populate_s2n_evp_hmac_state(struct s2n_evp_hmac_state *evp_hmac_state);

/*
* Properly allocates s2n_evp_hmac_state for CBMC proofs.
*/
struct s2n_evp_hmac_state *cbmc_allocate_s2n_evp_hmac_state();

/*
* Populates the fields of a pre-allocated s2n_hash_state for CBMC proofs.
*/
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19 changes: 0 additions & 19 deletions tests/cbmc/sources/make_common_datastructures.c
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Original file line number Diff line number Diff line change
Expand Up @@ -244,24 +244,6 @@ struct s2n_evp_digest* cbmc_allocate_s2n_evp_digest()
return evp_digest;
}

void cbmc_populate_s2n_evp_hmac_state(struct s2n_evp_hmac_state *evp_hmac_state)
{
CBMC_ENSURE_REF(evp_hmac_state);
cbmc_populate_s2n_evp_digest(&(evp_hmac_state->evp_digest));
if (s2n_libcrypto_is_awslc() || s2n_libcrypto_is_boringssl()) {
evp_hmac_state->ctx.hmac_ctx = malloc(sizeof(*(evp_hmac_state->ctx.hmac_ctx)));
} else {
evp_hmac_state->ctx.evp_pkey = malloc(sizeof(*(evp_hmac_state->ctx.evp_pkey)));
}
}

struct s2n_evp_hmac_state *cbmc_allocate_s2n_evp_hmac_state()
{
struct s2n_evp_hmac_state *evp_hmac_state = malloc(sizeof(*evp_hmac_state));
cbmc_populate_s2n_evp_hmac_state(evp_hmac_state);
return evp_hmac_state;
}

void cbmc_populate_s2n_hash_state(struct s2n_hash_state* state)
{
CBMC_ENSURE_REF(state);
Expand Down Expand Up @@ -715,7 +697,6 @@ void cbmc_populate_s2n_prf_working_space(struct s2n_prf_working_space *s2n_prf_w
* If required, this initialization should be done in the validation function.
*/
cbmc_populate_s2n_hmac_state(&(s2n_prf_working_space->p_hash.s2n_hmac));
cbmc_populate_s2n_evp_hmac_state(&(s2n_prf_working_space->p_hash.evp_hmac));
}

struct s2n_prf_working_space* cbmc_allocate_s2n_prf_working_space()
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192 changes: 19 additions & 173 deletions tls/s2n_prf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -40,8 +40,9 @@
#define S2N_LIBCRYPTO_SUPPORTS_TLS_PRF 0
#endif

/* The s2n p_hash implementation is abstracted to allow for separate implementations, using
* either s2n's formally verified HMAC or OpenSSL's EVP HMAC, for use by the TLS PRF. */
/* The s2n p_hash implementation is abstracted to allow for separate implementations.
* Currently the only implementation uses s2n-tls's custom HMAC implementation.
*/
struct s2n_p_hash_hmac {
int (*alloc)(struct s2n_prf_working_space *ws);
int (*init)(struct s2n_prf_working_space *ws, s2n_hmac_algorithm alg, struct s2n_blob *secret);
Expand Down Expand Up @@ -194,175 +195,9 @@ static int s2n_prf_sslv3(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 @@ -412,13 +247,20 @@ 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
* Both implementations have compatibility issues with one or more libcryptos.
*/
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 @@ -428,6 +270,7 @@ 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 @@ -494,6 +337,7 @@ 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 @@ -504,6 +348,7 @@ 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 @@ -517,6 +362,7 @@ 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
1 change: 0 additions & 1 deletion tls/s2n_prf.h
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Original file line number Diff line number Diff line change
Expand Up @@ -26,7 +26,6 @@

union p_hash_state {
struct s2n_hmac_state s2n_hmac;
struct s2n_evp_hmac_state evp_hmac;
};

struct s2n_prf_working_space {
Expand Down

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