/* * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved. * * Licensed under the Apache License, Version 2.0 (the "License"). * You may not use this file except in compliance with the License. * A copy of the License is located at * * http://aws.amazon.com/apache2.0 * * or in the "license" file accompanying this file. This file is distributed * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either * express or implied. See the License for the specific language governing * permissions and limitations under the License. */ #include "tls/s2n_tls13_certificate_verify.h" #include #include "crypto/s2n_hash.h" #include "error/s2n_errno.h" #include "stuffer/s2n_stuffer.h" #include "tls/s2n_async_pkey.h" #include "tls/s2n_connection.h" #include "tls/s2n_tls13_handshake.h" #include "utils/s2n_safety.h" /** * Specified in https://tools.ietf.org/html/rfc8446#section-4.4.3 * * Servers MUST send this message when authenticating via a certificate. * Clients MUST send this message whenever authenticating via a certificate. * When sent, this message MUST appear immediately after the Certificate * message and immediately prior to the Finished message. **/ /* 64 'space' characters (0x20) */ const uint8_t S2N_CERT_VERIFY_PREFIX[] = { 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20 }; /* 'TLS 1.3, server CertificateVerify' with 0x00 separator */ const uint8_t S2N_SERVER_CERT_VERIFY_CONTEXT[] = { 0x54, 0x4c, 0x53, 0x20, 0x31, 0x2e, 0x33, 0x2c, 0x20, 0x73, 0x65, 0x72, 0x76, 0x65, 0x72, 0x20, 0x43, 0x65, 0x72, 0x74, 0x69, 0x66, 0x69, 0x63, 0x61, 0x74, 0x65, 0x56, 0x65, 0x72, 0x69, 0x66, 0x79, 0x00 }; /* 'TLS 1.3, client CertificateVerify' with 0x00 separator */ const uint8_t S2N_CLIENT_CERT_VERIFY_CONTEXT[] = { 0x54, 0x4c, 0x53, 0x20, 0x31, 0x2e, 0x33, 0x2c, 0x20, 0x63, 0x6c, 0x69, 0x65, 0x6e, 0x74, 0x20, 0x43, 0x65, 0x72, 0x74, 0x69, 0x66, 0x69, 0x63, 0x61, 0x74, 0x65, 0x56, 0x65, 0x72, 0x69, 0x66, 0x79, 0x00 }; static int s2n_tls13_write_cert_verify_signature(struct s2n_connection *conn, const struct s2n_signature_scheme *chosen_sig_scheme); static int s2n_tls13_write_signature(struct s2n_connection *conn, struct s2n_blob *signature); static int s2n_tls13_generate_unsigned_cert_verify_content(struct s2n_connection *conn, struct s2n_stuffer *unsigned_content, s2n_mode mode); static int s2n_tls13_cert_read_and_verify_signature(struct s2n_connection *conn, const struct s2n_signature_scheme *chosen_sig_scheme); static uint8_t s2n_tls13_cert_verify_header_length(s2n_mode mode); int s2n_tls13_cert_verify_send(struct s2n_connection *conn) { S2N_ASYNC_PKEY_GUARD(conn); if (conn->mode == S2N_SERVER) { /* Write digital signature */ POSIX_GUARD(s2n_tls13_write_cert_verify_signature(conn, conn->handshake_params.server_cert_sig_scheme)); } else { /* Write digital signature */ POSIX_GUARD(s2n_tls13_write_cert_verify_signature(conn, conn->handshake_params.client_cert_sig_scheme)); } return 0; } int s2n_tls13_write_cert_verify_signature(struct s2n_connection *conn, const struct s2n_signature_scheme *chosen_sig_scheme) { POSIX_ENSURE_REF(conn->handshake_params.our_chain_and_key); /* Write the SignatureScheme out */ struct s2n_stuffer *out = &conn->handshake.io; POSIX_GUARD(s2n_stuffer_write_uint16(out, chosen_sig_scheme->iana_value)); DEFER_CLEANUP(struct s2n_hash_state message_hash = { 0 }, s2n_hash_free); POSIX_GUARD(s2n_hash_new(&message_hash)); POSIX_GUARD(s2n_hash_init(&message_hash, chosen_sig_scheme->hash_alg)); DEFER_CLEANUP(struct s2n_stuffer unsigned_content = { 0 }, s2n_stuffer_free); POSIX_GUARD(s2n_tls13_generate_unsigned_cert_verify_content(conn, &unsigned_content, conn->mode)); POSIX_GUARD(s2n_hash_update(&message_hash, unsigned_content.blob.data, s2n_stuffer_data_available(&unsigned_content))); S2N_ASYNC_PKEY_SIGN(conn, chosen_sig_scheme->sig_alg, &message_hash, s2n_tls13_write_signature); } int s2n_tls13_write_signature(struct s2n_connection *conn, struct s2n_blob *signature) { struct s2n_stuffer *out = &conn->handshake.io; POSIX_GUARD(s2n_stuffer_write_uint16(out, signature->size)); POSIX_GUARD(s2n_stuffer_write_bytes(out, signature->data, signature->size)); return 0; } int s2n_tls13_generate_unsigned_cert_verify_content(struct s2n_connection *conn, struct s2n_stuffer *unsigned_content, s2n_mode mode) { s2n_tls13_connection_keys(tls13_ctx, conn); uint8_t hash_digest_length = tls13_ctx.size; uint8_t digest_out[S2N_MAX_DIGEST_LEN]; /* Get current handshake hash */ POSIX_ENSURE_REF(conn->handshake.hashes); struct s2n_hash_state *hash_state = &conn->handshake.hashes->hash_workspace; POSIX_GUARD_RESULT(s2n_handshake_copy_hash_state(conn, tls13_ctx.hash_algorithm, hash_state)); POSIX_GUARD(s2n_hash_digest(hash_state, digest_out, hash_digest_length)); /* Concatenate the content to be signed/verified */ POSIX_GUARD(s2n_stuffer_alloc(unsigned_content, hash_digest_length + s2n_tls13_cert_verify_header_length(mode))); POSIX_GUARD(s2n_stuffer_write_bytes(unsigned_content, S2N_CERT_VERIFY_PREFIX, sizeof(S2N_CERT_VERIFY_PREFIX))); if (mode == S2N_CLIENT) { POSIX_GUARD(s2n_stuffer_write_bytes(unsigned_content, S2N_CLIENT_CERT_VERIFY_CONTEXT, sizeof(S2N_CLIENT_CERT_VERIFY_CONTEXT))); } else { POSIX_GUARD(s2n_stuffer_write_bytes(unsigned_content, S2N_SERVER_CERT_VERIFY_CONTEXT, sizeof(S2N_SERVER_CERT_VERIFY_CONTEXT))); } POSIX_GUARD(s2n_stuffer_write_bytes(unsigned_content, digest_out, hash_digest_length)); return 0; } uint8_t s2n_tls13_cert_verify_header_length(s2n_mode mode) { if (mode == S2N_CLIENT) { return sizeof(S2N_CERT_VERIFY_PREFIX) + sizeof(S2N_CLIENT_CERT_VERIFY_CONTEXT); } return sizeof(S2N_CERT_VERIFY_PREFIX) + sizeof(S2N_SERVER_CERT_VERIFY_CONTEXT); } int s2n_tls13_cert_verify_recv(struct s2n_connection *conn) { POSIX_GUARD_RESULT(s2n_signature_algorithm_recv(conn, &conn->handshake.io)); /* Read the rest of the signature and verify */ if (conn->mode == S2N_SERVER) { POSIX_GUARD(s2n_tls13_cert_read_and_verify_signature(conn, conn->handshake_params.client_cert_sig_scheme)); } else { POSIX_GUARD(s2n_tls13_cert_read_and_verify_signature(conn, conn->handshake_params.server_cert_sig_scheme)); } return 0; } int s2n_tls13_cert_read_and_verify_signature(struct s2n_connection *conn, const struct s2n_signature_scheme *chosen_sig_scheme) { struct s2n_stuffer *in = &conn->handshake.io; DEFER_CLEANUP(struct s2n_blob signed_content = { 0 }, s2n_free); DEFER_CLEANUP(struct s2n_stuffer unsigned_content = { 0 }, s2n_stuffer_free); DEFER_CLEANUP(struct s2n_hash_state message_hash = { 0 }, s2n_hash_free); POSIX_GUARD(s2n_hash_new(&message_hash)); /* Get signature size */ uint16_t signature_size = 0; POSIX_GUARD(s2n_stuffer_read_uint16(in, &signature_size)); S2N_ERROR_IF(signature_size > s2n_stuffer_data_available(in), S2N_ERR_BAD_MESSAGE); /* Get wire signature */ POSIX_GUARD(s2n_alloc(&signed_content, signature_size)); signed_content.size = signature_size; POSIX_GUARD(s2n_stuffer_read_bytes(in, signed_content.data, signature_size)); /* Verify signature. We send the opposite mode as we are trying to verify what was sent to us */ if (conn->mode == S2N_CLIENT) { POSIX_GUARD(s2n_tls13_generate_unsigned_cert_verify_content(conn, &unsigned_content, S2N_SERVER)); } else { POSIX_GUARD(s2n_tls13_generate_unsigned_cert_verify_content(conn, &unsigned_content, S2N_CLIENT)); } POSIX_GUARD(s2n_hash_init(&message_hash, chosen_sig_scheme->hash_alg)); POSIX_GUARD(s2n_hash_update(&message_hash, unsigned_content.blob.data, s2n_stuffer_data_available(&unsigned_content))); if (conn->mode == S2N_CLIENT) { POSIX_GUARD(s2n_pkey_verify(&conn->handshake_params.server_public_key, chosen_sig_scheme->sig_alg, &message_hash, &signed_content)); } else { POSIX_GUARD(s2n_pkey_verify(&conn->handshake_params.client_public_key, chosen_sig_scheme->sig_alg, &message_hash, &signed_content)); } return 0; }