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Address possible vulnerability in preauth lengths in hybrid KEM #2

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Address possible vulnerability in preauth lengths in hybrid KEM #2

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40 changes: 38 additions & 2 deletions kexoqsecdh.c
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Original file line number Diff line number Diff line change
Expand Up @@ -183,6 +183,8 @@ static int kex_kem_generic_with_ec_enc(OQS_KEM *kem,
struct sshbuf *ecdh_client_blob = NULL;
struct sshbuf *ecdh_server_blob = NULL;
struct sshbuf *ecdh_shared_secret;
size_t client_blob_len = 0;
size_t ecdh_part_len = 0;
u_char hash[SSH_DIGEST_MAX_LENGTH];
int r = SSH_ERR_INTERNAL_ERROR;
*server_blobp = NULL;
Expand All @@ -197,6 +199,12 @@ static int kex_kem_generic_with_ec_enc(OQS_KEM *kem,
goto out;
}*/

client_blob_len = sshbuf_len(client_blob);
if (client_blob_len < kem->length_public_key) {
r = SSH_ERR_SIGNATURE_INVALID;
goto out;
}

/* get a pointer to the client PQC public key */
client_pub = sshbuf_ptr(client_blob);
/* allocate buffer for concatenation of KEM key and ECDH shared key */
Expand Down Expand Up @@ -230,7 +238,17 @@ static int kex_kem_generic_with_ec_enc(OQS_KEM *kem,
goto out;
}

ecdh_client_blob = sshbuf_from(client_pub + kem->length_public_key, sshbuf_len(client_blob) - kem->length_public_key);
ecdh_part_len = client_blob_len - kem->length_public_key;
if (ecdh_part_len == 0) {
r = SSH_ERR_SIGNATURE_INVALID;
goto out;
}
ecdh_client_blob = sshbuf_from(client_pub + kem->length_public_key,
ecdh_part_len);
if (ecdh_client_blob == NULL) {
r = SSH_ERR_ALLOC_FAIL;
goto out;
}
/* generate ecdh key pair, store server ecdh public key after KEM ciphertext
as done in kex_ecdh_enc(...) */
if ((ecdh_server_key = EC_KEY_new_by_curve_name(kex->ec_nid)) == NULL) {
Expand Down Expand Up @@ -295,6 +313,8 @@ static int kex_kem_generic_with_ec_dec(OQS_KEM *kem,
struct sshbuf *ecdh_shared_secret;
struct sshbuf *ecdh_server_blob = NULL;
u_char hash[SSH_DIGEST_MAX_LENGTH];
size_t server_blob_len = 0;
size_t ecdh_part_len = 0;
int r = SSH_ERR_INTERNAL_ERROR;
*shared_secretp = NULL;

Expand All @@ -307,6 +327,12 @@ static int kex_kem_generic_with_ec_dec(OQS_KEM *kem,
goto out;
} */

server_blob_len = sshbuf_len(server_blob);
if (server_blob_len < kem->length_ciphertext) {
r = SSH_ERR_SIGNATURE_INVALID;
goto out;
}

/* get a pointer to the server PQC ciphertext */
ciphertext = sshbuf_ptr(server_blob);

Expand All @@ -326,7 +352,17 @@ static int kex_kem_generic_with_ec_dec(OQS_KEM *kem,

/* derive the ecdh shared key, using 2nd part of server_blob
as done in kex_ecdh_dec(...) */
ecdh_server_blob = sshbuf_from(ciphertext + kem->length_ciphertext, sshbuf_len(server_blob) - kem->length_ciphertext);
ecdh_part_len = server_blob_len - kem->length_ciphertext;
if (ecdh_part_len == 0) {
r = SSH_ERR_SIGNATURE_INVALID;
goto out;
}
ecdh_server_blob = sshbuf_from(ciphertext + kem->length_ciphertext,
ecdh_part_len);
if (ecdh_server_blob == NULL) {
r = SSH_ERR_ALLOC_FAIL;
goto out;
}

if ((r = kex_ecdh_dec_key_group(kex, ecdh_server_blob, kex->ec_client_key,
kex->ec_group, &ecdh_shared_secret)) != 0)
Expand Down
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