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Disable RC4 when built with Openssl-3.0 #3982

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Disable RC4 when built with Openssl-3.0 #3982

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7ed91eb
Disable RC4 when built with Openssl-3.0
lrstewart May 4, 2023
c914f3d
Change usage guide wording
lrstewart May 5, 2023
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40 changes: 1 addition & 39 deletions crypto/s2n_libcrypto.c
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Original file line number Diff line number Diff line change
Expand Up @@ -17,17 +17,13 @@

#include <openssl/crypto.h>
#include <openssl/opensslv.h>
#include <string.h>

#include "crypto/s2n_crypto.h"
#include "crypto/s2n_fips.h"
#include "crypto/s2n_openssl.h"
#include "utils/s2n_safety.h"
#include "utils/s2n_safety_macros.h"
#if S2N_OPENSSL_VERSION_AT_LEAST(3, 0, 0)
#include <openssl/provider.h>
#endif

#include <string.h>

/* Note: OpenSSL 1.0.2 -> 1.1.0 implemented a new API to get the version number
* and version name. We have to handle that by using old functions
Expand Down Expand Up @@ -149,40 +145,6 @@ bool s2n_libcrypto_is_libressl()
#endif
}

S2N_RESULT s2n_libcrypto_init(void)
{
#if S2N_OPENSSL_VERSION_AT_LEAST(3, 0, 0)
RESULT_ENSURE(OSSL_PROVIDER_load(NULL, "default") != NULL, S2N_ERR_OSSL_PROVIDER);
#ifdef S2N_LIBCRYPTO_SUPPORTS_EVP_RC4
/* needed to support RC4 algorithm
* https://www.openssl.org/docs/man3.0/man7/OSSL_PROVIDER-legacy.html
*/
RESULT_ENSURE(OSSL_PROVIDER_load(NULL, "legacy") != NULL, S2N_ERR_OSSL_PROVIDER);
#endif
#endif

return S2N_RESULT_OK;
}

#if S2N_OPENSSL_VERSION_AT_LEAST(3, 0, 0)
int s2n_libcrypto_cleanup_cb(OSSL_PROVIDER *provider, void *cbdata)
{
return OSSL_PROVIDER_unload(provider);
}

S2N_RESULT s2n_libcrypto_cleanup(void)
{
RESULT_GUARD_OSSL(OSSL_PROVIDER_do_all(NULL, *s2n_libcrypto_cleanup_cb, NULL), S2N_ERR_ATEXIT);

return S2N_RESULT_OK;
}
#else
S2N_RESULT s2n_libcrypto_cleanup(void)
{
return S2N_RESULT_OK;
}
#endif

/* Performs various checks to validate that the libcrypto used at compile-time
* is the same libcrypto being used at run-time.
*/
Expand Down
2 changes: 0 additions & 2 deletions crypto/s2n_libcrypto.h
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Expand Up @@ -17,6 +17,4 @@

#include "utils/s2n_result.h"

S2N_RESULT s2n_libcrypto_init(void);
S2N_RESULT s2n_libcrypto_validate_runtime(void);
S2N_RESULT s2n_libcrypto_cleanup(void);
61 changes: 19 additions & 42 deletions crypto/s2n_stream_cipher_rc4.c
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Expand Up @@ -21,20 +21,30 @@
#include "utils/s2n_blob.h"
#include "utils/s2n_safety.h"

static uint8_t s2n_stream_cipher_rc4_available()
static const EVP_CIPHER *s2n_evp_rc4()
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It's hard to tell from the docs but does this EVP_CIPHER need to be free'd with EVP_CIPHER_free? Or is it a global?

{
#ifdef S2N_LIBCRYPTO_SUPPORTS_EVP_RC4
return EVP_rc4();
Comment on lines 26 to +27
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should this also check for Openssl-3?

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Nope. It's not testing for support, just limiting the blast radius of the #if we need to check for the existence of the EVP_rc4() symbol.

#else
return NULL;
#endif
}

static uint8_t s2n_stream_cipher_rc4_available()
{
if (s2n_is_in_fips_mode()) {
return 0;
} else {
return (EVP_rc4() ? 1 : 0);
}
#else
return 0;
#endif /* S2N_LIBCRYPTO_SUPPORTS_EVP_RC4 */
/* RC4 MIGHT be available in Openssl-3.0, depending on whether or not the
* "legacy" provider is loaded. However, for simplicity, assume that RC4
* is unavailable.
*/
if (S2N_OPENSSL_VERSION_AT_LEAST(3, 0, 0)) {
return 0;
}
return (s2n_evp_rc4() ? 1 : 0);
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}

#ifdef S2N_LIBCRYPTO_SUPPORTS_EVP_RC4
static int s2n_stream_cipher_rc4_encrypt(struct s2n_session_key *key, struct s2n_blob *in, struct s2n_blob *out)
{
POSIX_ENSURE_GTE(out->size, in->size);
Expand Down Expand Up @@ -64,15 +74,15 @@ static int s2n_stream_cipher_rc4_decrypt(struct s2n_session_key *key, struct s2n
static int s2n_stream_cipher_rc4_set_encryption_key(struct s2n_session_key *key, struct s2n_blob *in)
{
POSIX_ENSURE_EQ(in->size, 16);
POSIX_GUARD_OSSL(EVP_EncryptInit_ex(key->evp_cipher_ctx, EVP_rc4(), NULL, in->data, NULL), S2N_ERR_KEY_INIT);
POSIX_GUARD_OSSL(EVP_EncryptInit_ex(key->evp_cipher_ctx, s2n_evp_rc4(), NULL, in->data, NULL), S2N_ERR_KEY_INIT);

return 0;
}

static int s2n_stream_cipher_rc4_set_decryption_key(struct s2n_session_key *key, struct s2n_blob *in)
{
POSIX_ENSURE_EQ(in->size, 16);
POSIX_GUARD_OSSL(EVP_DecryptInit_ex(key->evp_cipher_ctx, EVP_rc4(), NULL, in->data, NULL), S2N_ERR_KEY_INIT);
POSIX_GUARD_OSSL(EVP_DecryptInit_ex(key->evp_cipher_ctx, s2n_evp_rc4(), NULL, in->data, NULL), S2N_ERR_KEY_INIT);

return 0;
}
Expand All @@ -90,39 +100,6 @@ static int s2n_stream_cipher_rc4_destroy_key(struct s2n_session_key *key)

return 0;
}
#else

static int s2n_stream_cipher_rc4_encrypt(struct s2n_session_key *key, struct s2n_blob *in, struct s2n_blob *out)
{
POSIX_BAIL(S2N_ERR_UNIMPLEMENTED);
}

static int s2n_stream_cipher_rc4_decrypt(struct s2n_session_key *key, struct s2n_blob *in, struct s2n_blob *out)
{
POSIX_BAIL(S2N_ERR_UNIMPLEMENTED);
}

static int s2n_stream_cipher_rc4_set_encryption_key(struct s2n_session_key *key, struct s2n_blob *in)
{
POSIX_BAIL(S2N_ERR_UNIMPLEMENTED);
}

static int s2n_stream_cipher_rc4_set_decryption_key(struct s2n_session_key *key, struct s2n_blob *in)
{
POSIX_BAIL(S2N_ERR_UNIMPLEMENTED);
}

static int s2n_stream_cipher_rc4_init(struct s2n_session_key *key)
{
POSIX_BAIL(S2N_ERR_UNIMPLEMENTED);
}

static int s2n_stream_cipher_rc4_destroy_key(struct s2n_session_key *key)
{
POSIX_BAIL(S2N_ERR_UNIMPLEMENTED);
}

#endif /* S2N_LIBCRYPTO_SUPPORTS_EVP_RC4 */

const struct s2n_cipher s2n_rc4 = {
.type = S2N_STREAM,
Expand Down
6 changes: 6 additions & 0 deletions docs/USAGE-GUIDE.md
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Expand Up @@ -179,6 +179,12 @@ cd ../../ # root of project
make
```

### Available algorithms
Not all algorithms are available from all versions of Openssl:
* ChaChaPoly is not supported before Openssl-1.1.1
* RSA-PSS is not supported before Openssl-1.1.1
* RC4 is not supported with Openssl-3.0 or later.

## Building s2n-tls with LibreSSL

To build s2n-tls with LibreSSL, do the following:
Expand Down
21 changes: 15 additions & 6 deletions tests/unit/s2n_rc4_test.c
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Expand Up @@ -20,6 +20,7 @@
#include "crypto/s2n_cipher.h"
#include "crypto/s2n_fips.h"
#include "crypto/s2n_hmac.h"
#include "crypto/s2n_openssl.h"
#include "s2n_test.h"
#include "stuffer/s2n_stuffer.h"
#include "testlib/s2n_testlib.h"
Expand All @@ -32,6 +33,16 @@ int main(int argc, char **argv)
{
BEGIN_TEST();

/* Test Openssl-3.0 does not support RC4 */
if (S2N_OPENSSL_VERSION_AT_LEAST(3, 0, 0)) {
EXPECT_FALSE(s2n_rc4.is_available());
}

/* Test FIPS does not support RC4 */
if (s2n_is_in_fips_mode()) {
EXPECT_FALSE(s2n_rc4.is_available());
}

struct s2n_connection *conn;
uint8_t mac_key[] = "sample mac key";
uint8_t rc4_key[] = "123456789012345";
Expand All @@ -57,9 +68,9 @@ int main(int argc, char **argv)

/* test the RC4 cipher with a SHA1 hash */
conn->secure->cipher_suite->record_alg = &s2n_record_alg_rc4_sha;
EXPECT_SUCCESS(conn->secure->cipher_suite->record_alg->cipher->init(&conn->secure->server_key));
EXPECT_SUCCESS(conn->secure->cipher_suite->record_alg->cipher->init(&conn->secure->client_key));
if (conn->secure->cipher_suite->record_alg->cipher->is_available()) {
EXPECT_SUCCESS(conn->secure->cipher_suite->record_alg->cipher->init(&conn->secure->server_key));
EXPECT_SUCCESS(conn->secure->cipher_suite->record_alg->cipher->init(&conn->secure->client_key));
EXPECT_SUCCESS(conn->secure->cipher_suite->record_alg->cipher->set_decryption_key(&conn->secure->client_key, &key_iv));
EXPECT_SUCCESS(conn->secure->cipher_suite->record_alg->cipher->set_encryption_key(&conn->secure->server_key, &key_iv));
EXPECT_SUCCESS(s2n_hmac_init(&conn->secure->client_record_mac, S2N_HMAC_SHA1, mac_key, sizeof(mac_key)));
Expand Down Expand Up @@ -119,10 +130,8 @@ int main(int argc, char **argv)
EXPECT_SUCCESS(conn->secure->cipher_suite->record_alg->cipher->destroy_key(&conn->secure->client_key));
EXPECT_SUCCESS(s2n_connection_free(conn));
} else {
EXPECT_FAILURE_WITH_ERRNO(conn->secure->cipher_suite->record_alg->cipher->init(&conn->secure->server_key), S2N_ERR_UNIMPLEMENTED);
EXPECT_FAILURE_WITH_ERRNO(conn->secure->cipher_suite->record_alg->cipher->init(&conn->secure->client_key), S2N_ERR_UNIMPLEMENTED);
EXPECT_FAILURE_WITH_ERRNO(conn->secure->cipher_suite->record_alg->cipher->set_decryption_key(&conn->secure->client_key, &key_iv), S2N_ERR_UNIMPLEMENTED);
EXPECT_FAILURE_WITH_ERRNO(conn->secure->cipher_suite->record_alg->cipher->set_encryption_key(&conn->secure->server_key, &key_iv), S2N_ERR_UNIMPLEMENTED);
EXPECT_FAILURE(conn->secure->cipher_suite->record_alg->cipher->set_decryption_key(&conn->secure->client_key, &key_iv));
EXPECT_FAILURE(conn->secure->cipher_suite->record_alg->cipher->set_encryption_key(&conn->secure->server_key, &key_iv));
}

END_TEST();
Expand Down
2 changes: 0 additions & 2 deletions utils/s2n_init.c
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Expand Up @@ -66,7 +66,6 @@ int s2n_init(void)
POSIX_GUARD(s2n_mem_init());
/* Must run before any init method that calls libcrypto methods. */
POSIX_GUARD_RESULT(s2n_locking_init());
POSIX_GUARD_RESULT(s2n_libcrypto_init());
POSIX_GUARD(s2n_fips_init());
POSIX_GUARD_RESULT(s2n_rand_init());
POSIX_GUARD(s2n_cipher_suites_init());
Expand Down Expand Up @@ -100,7 +99,6 @@ static bool s2n_cleanup_atexit_impl(void)
bool cleaned_up = s2n_result_is_ok(s2n_cipher_suites_cleanup())
&& s2n_result_is_ok(s2n_rand_cleanup_thread())
&& s2n_result_is_ok(s2n_rand_cleanup())
&& s2n_result_is_ok(s2n_libcrypto_cleanup())
&& s2n_result_is_ok(s2n_locking_cleanup())
&& (s2n_mem_cleanup() == S2N_SUCCESS);

Expand Down