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authorJakub Jelen <jjelen@redhat.com>2018-10-08 13:24:49 +0200
committerAndreas Schneider <asn@cryptomilk.org>2018-10-09 12:05:40 +0200
commit46090facbae8c8292d2775546082ccbd5e56fbd1 (patch)
tree3e6875a6e353d9d496972f0756f220446f082db2 /src/libcrypto.c
parent777786d76c83b017ce6936bd15aa3413fd65bcca (diff)
downloadlibssh-46090facbae8c8292d2775546082ccbd5e56fbd1.tar.gz
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libcrypto: Implement OpenSSH-compatible AES-GCM ciphers using OpenSSL
The commit also propares the internals throughout the code base for the inclusion of a new AEAD cipher, because previously, the source code counted only with chacha20-poly1305 cipher, which is very specific in many cases. The SSH_HMAC_AEAD_GCM mac algorithm is not actually used, but the name needed to be defined so we can match in the algorithms selection per OpenSSH specification (MACs are ignored in case GCM is select as a cipher [1]). If the provided OpenSSL does not provide EVP_aes_128_gcm() function, the AES-GCM ciphers will not be compiled in. [1] https://cvsweb.openbsd.org/src/usr.bin/ssh/PROTOCOL.chacha20poly1305?annotate=HEAD Signed-off-by: Jakub Jelen <jjelen@redhat.com> Reviewed-by: Andreas Schneider <asn@cryptomilk.org>
Diffstat (limited to 'src/libcrypto.c')
-rw-r--r--src/libcrypto.c247
1 files changed, 247 insertions, 0 deletions
diff --git a/src/libcrypto.c b/src/libcrypto.c
index ffbb1171..35b73b9f 100644
--- a/src/libcrypto.c
+++ b/src/libcrypto.c
@@ -492,6 +492,19 @@ static void evp_cipher_init(struct ssh_cipher_struct *cipher) {
SSH_LOG(SSH_LOG_WARNING, "This cipher is not available in evp_cipher_init");
break;
#endif
+#ifdef HAVE_OPENSSL_EVP_AES_GCM
+ case SSH_AEAD_AES128_GCM:
+ cipher->cipher = EVP_aes_128_gcm();
+ break;
+ case SSH_AEAD_AES256_GCM:
+ cipher->cipher = EVP_aes_256_gcm();
+ break;
+#else
+ case SSH_AEAD_AES128_GCM:
+ case SSH_AEAD_AES256_GCM:
+ SSH_LOG(SSH_LOG_WARNING, "This cipher is not available in evp_cipher_init");
+ break;
+#endif /* HAVE_OPENSSL_EVP_AES_GCM */
case SSH_3DES_CBC:
cipher->cipher = EVP_des_ede3_cbc();
break;
@@ -499,6 +512,9 @@ static void evp_cipher_init(struct ssh_cipher_struct *cipher) {
cipher->cipher = EVP_bf_cbc();
break;
/* ciphers not using EVP */
+ case SSH_AEAD_CHACHA20_POLY1305:
+ SSH_LOG(SSH_LOG_WARNING, "The ChaCha cipher can not be handled here");
+ break;
case SSH_NO_CIPHER:
SSH_LOG(SSH_LOG_WARNING, "No valid ciphertype found");
break;
@@ -518,6 +534,22 @@ static int evp_cipher_set_encrypt_key(struct ssh_cipher_struct *cipher,
SSH_LOG(SSH_LOG_WARNING, "EVP_EncryptInit_ex failed");
return SSH_ERROR;
}
+
+#ifdef HAVE_OPENSSL_EVP_AES_GCM
+ /* For AES-GCM we need to set IV in specific way */
+ if (cipher->ciphertype == SSH_AEAD_AES128_GCM ||
+ cipher->ciphertype == SSH_AEAD_AES256_GCM) {
+ rc = EVP_CIPHER_CTX_ctrl(cipher->ctx,
+ EVP_CTRL_GCM_SET_IV_FIXED,
+ -1,
+ (u_char *)IV);
+ if (rc != 1) {
+ SSH_LOG(SSH_LOG_WARNING, "EVP_CTRL_GCM_SET_IV_FIXED failed");
+ return SSH_ERROR;
+ }
+ }
+#endif /* HAVE_OPENSSL_EVP_AES_GCM */
+
EVP_CIPHER_CTX_set_padding(cipher->ctx, 0);
return SSH_OK;
@@ -535,6 +567,22 @@ static int evp_cipher_set_decrypt_key(struct ssh_cipher_struct *cipher,
SSH_LOG(SSH_LOG_WARNING, "EVP_DecryptInit_ex failed");
return SSH_ERROR;
}
+
+#ifdef HAVE_OPENSSL_EVP_AES_GCM
+ /* For AES-GCM we need to set IV in specific way */
+ if (cipher->ciphertype == SSH_AEAD_AES128_GCM ||
+ cipher->ciphertype == SSH_AEAD_AES256_GCM) {
+ rc = EVP_CIPHER_CTX_ctrl(cipher->ctx,
+ EVP_CTRL_GCM_SET_IV_FIXED,
+ -1,
+ (u_char *)IV);
+ if (rc != 1) {
+ SSH_LOG(SSH_LOG_WARNING, "EVP_CTRL_GCM_SET_IV_FIXED failed");
+ return SSH_ERROR;
+ }
+ }
+#endif /* HAVE_OPENSSL_EVP_AES_GCM */
+
EVP_CIPHER_CTX_set_padding(cipher->ctx, 0);
return SSH_OK;
@@ -643,6 +691,175 @@ static void aes_ctr_cleanup(struct ssh_cipher_struct *cipher){
#endif /* HAVE_OPENSSL_EVP_AES_CTR */
+#ifdef HAVE_OPENSSL_EVP_AES_GCM
+static int
+evp_cipher_aead_get_length(struct ssh_cipher_struct *cipher,
+ void *in,
+ uint8_t *out,
+ size_t len,
+ uint64_t seq)
+{
+ (void)seq;
+
+ /* The length is not encrypted: Copy it to the result buffer */
+ memcpy(out, in, len);
+
+ return SSH_OK;
+}
+
+static void
+evp_cipher_aead_encrypt(struct ssh_cipher_struct *cipher,
+ void *in,
+ void *out,
+ size_t len,
+ uint8_t *tag,
+ uint64_t seq)
+{
+ size_t authlen, aadlen;
+ u_char lastiv[1];
+ int outlen = 0;
+ int rc;
+
+ (void) seq;
+
+ aadlen = cipher->lenfield_blocksize;
+ authlen = cipher->tag_size;
+
+ /* increment IV */
+ rc = EVP_CIPHER_CTX_ctrl(cipher->ctx,
+ EVP_CTRL_GCM_IV_GEN,
+ 1,
+ lastiv);
+ if (rc == 0) {
+ SSH_LOG(SSH_LOG_WARNING, "EVP_CTRL_GCM_IV_GEN failed");
+ return;
+ }
+
+ /* Pass over the authenticated data (not encrypted) */
+ rc = EVP_EncryptUpdate(cipher->ctx,
+ NULL,
+ &outlen,
+ (unsigned char *)in,
+ aadlen);
+ if (rc == 0 || outlen != aadlen) {
+ SSH_LOG(SSH_LOG_WARNING, "Failed to pass authenticated data");
+ return;
+ }
+ memcpy(out, in, aadlen);
+
+ /* Encrypt the rest of the data */
+ rc = EVP_EncryptUpdate(cipher->ctx,
+ (unsigned char *)out + aadlen,
+ &outlen,
+ (unsigned char *)in + aadlen,
+ len - aadlen);
+ if (rc != 1 || outlen != len - aadlen) {
+ SSH_LOG(SSH_LOG_WARNING, "EVP_EncryptUpdate failed");
+ return;
+ }
+
+ /* compute tag */
+ rc = EVP_EncryptFinal(cipher->ctx,
+ NULL,
+ &outlen);
+ if (rc < 0) {
+ SSH_LOG(SSH_LOG_WARNING, "EVP_EncryptFinal failed: Failed to create a tag");
+ return;
+ }
+
+ rc = EVP_CIPHER_CTX_ctrl(cipher->ctx,
+ EVP_CTRL_GCM_GET_TAG,
+ authlen,
+ (unsigned char *)tag);
+ if (rc != 1) {
+ SSH_LOG(SSH_LOG_WARNING, "EVP_CTRL_GCM_GET_TAG failed");
+ return;
+ }
+}
+
+static int
+evp_cipher_aead_decrypt(struct ssh_cipher_struct *cipher,
+ void *complete_packet,
+ uint8_t *out,
+ size_t encrypted_size,
+ uint64_t seq)
+{
+ size_t authlen, aadlen;
+ u_char lastiv[1];
+ int outlen = 0;
+ int rc = 0;
+
+ (void)seq;
+
+ aadlen = cipher->lenfield_blocksize;
+ authlen = cipher->tag_size;
+
+ /* increment IV */
+ rc = EVP_CIPHER_CTX_ctrl(cipher->ctx,
+ EVP_CTRL_GCM_IV_GEN,
+ 1,
+ lastiv);
+ if (rc == 0) {
+ SSH_LOG(SSH_LOG_WARNING, "EVP_CTRL_GCM_IV_GEN failed");
+ return SSH_ERROR;
+ }
+
+ /* set tag for authentication */
+ rc = EVP_CIPHER_CTX_ctrl(cipher->ctx,
+ EVP_CTRL_GCM_SET_TAG,
+ authlen,
+ (unsigned char *)complete_packet + aadlen + encrypted_size);
+ if (rc == 0) {
+ SSH_LOG(SSH_LOG_WARNING, "EVP_CTRL_GCM_SET_TAG failed");
+ return SSH_ERROR;
+ }
+
+ /* Pass over the authenticated data (not encrypted) */
+ rc = EVP_DecryptUpdate(cipher->ctx,
+ NULL,
+ &outlen,
+ (unsigned char *)complete_packet,
+ aadlen);
+ if (rc == 0) {
+ SSH_LOG(SSH_LOG_WARNING, "Failed to pass authenticated data");
+ return SSH_ERROR;
+ }
+ /* Do not copy the length to the target buffer, because it is already processed */
+ //memcpy(out, complete_packet, aadlen);
+
+ /* Decrypt the rest of the data */
+ rc = EVP_DecryptUpdate(cipher->ctx,
+ (unsigned char *)out,
+ &outlen,
+ (unsigned char *)complete_packet + aadlen,
+ encrypted_size /* already substracted aadlen*/);
+ if (rc != 1) {
+ SSH_LOG(SSH_LOG_WARNING, "EVP_DecryptUpdate failed");
+ return SSH_ERROR;
+ }
+
+ if (outlen != (int)encrypted_size) {
+ SSH_LOG(SSH_LOG_WARNING,
+ "EVP_DecryptUpdate: output size %d for %zd in",
+ outlen,
+ encrypted_size);
+ return SSH_ERROR;
+ }
+
+ /* verify tag */
+ rc = EVP_DecryptFinal(cipher->ctx,
+ NULL,
+ &outlen);
+ if (rc < 0) {
+ SSH_LOG(SSH_LOG_WARNING, "EVP_DecryptFinal failed: Failed authentication");
+ return SSH_ERROR;
+ }
+
+ return SSH_OK;
+}
+
+#endif /* HAVE_OPENSSL_EVP_AES_GCM */
+
/*
* The table of supported ciphers
*/
@@ -766,6 +983,36 @@ static struct ssh_cipher_struct ssh_ciphertab[] = {
.decrypt = evp_cipher_decrypt,
.cleanup = evp_cipher_cleanup
},
+#ifdef HAVE_OPENSSL_EVP_AES_GCM
+ {
+ .name = "aes128-gcm@openssh.com",
+ .blocksize = AES_BLOCK_SIZE,
+ .lenfield_blocksize = 4, /* not encrypted, but authenticated */
+ .ciphertype = SSH_AEAD_AES128_GCM,
+ .keysize = 128,
+ .tag_size = AES_GCM_TAGLEN,
+ .set_encrypt_key = evp_cipher_set_encrypt_key,
+ .set_decrypt_key = evp_cipher_set_decrypt_key,
+ .aead_encrypt = evp_cipher_aead_encrypt,
+ .aead_decrypt_length = evp_cipher_aead_get_length,
+ .aead_decrypt = evp_cipher_aead_decrypt,
+ .cleanup = evp_cipher_cleanup
+ },
+ {
+ .name = "aes256-gcm@openssh.com",
+ .blocksize = AES_BLOCK_SIZE,
+ .lenfield_blocksize = 4, /* not encrypted, but authenticated */
+ .ciphertype = SSH_AEAD_AES256_GCM,
+ .keysize = 256,
+ .tag_size = AES_GCM_TAGLEN,
+ .set_encrypt_key = evp_cipher_set_encrypt_key,
+ .set_decrypt_key = evp_cipher_set_decrypt_key,
+ .aead_encrypt = evp_cipher_aead_encrypt,
+ .aead_decrypt_length = evp_cipher_aead_get_length,
+ .aead_decrypt = evp_cipher_aead_decrypt,
+ .cleanup = evp_cipher_cleanup
+ },
+#endif /* HAVE_OPENSSL_EVP_AES_GCM */
#endif /* HAS_AES */
#ifdef HAS_DES
{