From 858618e7e037559b75b0bfca4d30440f9515b888 Mon Sep 17 00:00:00 2001 From: Nick Mathewson Date: Mon, 25 May 2015 17:12:49 -0400 Subject: [PATCH] Add new functions to extract {client,server}_random, master_key Tor uses these values to implement a low-rent clone of RFC 5705 (which, in our defense, we came up with before RFC 5705 existed). But now that ssl_st is opaque, we need another way to get at them. Includes documentation, with suitable warnings about not actually using these functions. Signed-off-by: Nick Mathewson Signed-off-by: Matt Caswell Reviewed-by: Tim Hudson --- doc/ssl/SSL_get_client_random.pod | 73 +++++++++++++++++++++++++++++++ include/openssl/ssl.h | 4 ++ ssl/ssl_lib.c | 31 +++++++++++++ 3 files changed, 108 insertions(+) create mode 100644 doc/ssl/SSL_get_client_random.pod diff --git a/doc/ssl/SSL_get_client_random.pod b/doc/ssl/SSL_get_client_random.pod new file mode 100644 index 0000000000..e31d3f0a28 --- /dev/null +++ b/doc/ssl/SSL_get_client_random.pod @@ -0,0 +1,73 @@ +=pod + +=head1 NAME + +SSL_get_client_random, SSL_get_server_random, SSL_SESSION_get_master_key - retrieve internal TLS/SSL random values and master key + +=head1 SYNOPSIS + + #include + + int SSL_get_client_random(const SSL *ssl, unsigned char *out, int outlen); + int SSL_get_server_random(const SSL *ssl, unsigned char *out, int outlen); + int SSL_SESSION_get_master_key(const SSL_SESSION *session, unsigned char *out, int outlen); + +=head1 DESCRIPTION + +SSL_get_client_random() extracts the random value sent from the client +to the server during the initial SSL/TLS handshake. It copies this +value into the buffer provided in B, which must have at least +B bytes available. It returns the total number of bytes that were +actually copied. +If B is less than zero, SSL_get_client_random() copies nothing, and +returns the total size of the client_random value. + +SSL_get_server_random() behaves the same, but extracts the random value +sent from the server to the client during the initial SSL/TLS handshake. + +SSL_SESSION_get_master_key() behaves the same, but extracts the master +secret used to guarantee the security of the SSL/TLS session. This one +can be dangerous if misused; see NOTES below. + + +=head1 NOTES + +You probably shouldn't use these functions. + +These functions expose internal values from the TLS handshake, for +use in low-level protocols. You probably should not use them, unless +you are implementing something that needs access to the internal protocol +details. + +Despite the names of SSL_get_client_random() and SSL_get_server_random(), they +ARE NOT random number generators. Instead, they return the mostly-random values that +were already generated and used in the TLS protoccol. Using them +in place of RAND_bytes() would be grossly foolish. + +The security of your TLS session depends on keeping the master key secret: +do not expose it, or any information about it, to anybody. +If you need to calculate another secret value that depends on the master +secret, you should probably use SSL_export_keying_material() instead, and +forget that you ever saw these functions. + +Finally, though the "client_random" and "server_random" values are called +"random", many TLS implementations will generate four bytes of those +values based on their view of the current time. + + +=head1 RETURN VALUES + +If B is at least 0, these functions return the number of bytes +actually copied, which will be less than or equal to B. + +If B is less than 0, these functions return the maximum number +of bytes they would copy--that is, the length of the underlying field. + +=head1 SEE ALSO + +L, +L, +L + + +=cut diff --git a/include/openssl/ssl.h b/include/openssl/ssl.h index 5de33e9305..e52fbb5a13 100644 --- a/include/openssl/ssl.h +++ b/include/openssl/ssl.h @@ -1652,6 +1652,10 @@ void SSL_set_state(SSL *ssl, int state); void SSL_set_verify_result(SSL *ssl, long v); __owur long SSL_get_verify_result(const SSL *ssl); +__owur int SSL_get_client_random(const SSL *ssl, unsigned char *out, int outlen); +__owur int SSL_get_server_random(const SSL *ssl, unsigned char *out, int outlen); +__owur int SSL_SESSION_get_master_key(const SSL_SESSION *ssl, unsigned char *out, int outlen); + __owur int SSL_set_ex_data(SSL *ssl, int idx, void *data); void *SSL_get_ex_data(const SSL *ssl, int idx); __owur int SSL_get_ex_new_index(long argl, void *argp, CRYPTO_EX_new *new_func, diff --git a/ssl/ssl_lib.c b/ssl/ssl_lib.c index 0b4b58e0f8..081f27a73e 100644 --- a/ssl/ssl_lib.c +++ b/ssl/ssl_lib.c @@ -2897,6 +2897,37 @@ long SSL_get_verify_result(const SSL *ssl) return (ssl->verify_result); } +int SSL_get_client_random(const SSL *ssl, unsigned char *out, int outlen) +{ + if (outlen < 0) + return sizeof(ssl->s3->client_random); + if (outlen > sizeof(ssl->s3->client_random)) + outlen = sizeof(ssl->s3->client_random); + memcpy(out, ssl->s3->client_random, outlen); + return (outlen); +} + +int SSL_get_server_random(const SSL *ssl, unsigned char *out, int outlen) +{ + if (outlen < 0) + return sizeof(ssl->s3->server_random); + if (outlen > sizeof(ssl->s3->server_random)) + outlen = sizeof(ssl->s3->server_random); + memcpy(out, ssl->s3->server_random, outlen); + return (outlen); +} + +int SSL_SESSION_get_master_key(const SSL_SESSION *session, + unsigned char *out, int outlen) +{ + if (outlen < 0) + return session->master_key_length; + if (outlen > session->master_key_length) + outlen = session->master_key_length; + memcpy(out, session->master_key, outlen); + return (outlen); +} + int SSL_get_ex_new_index(long argl, void *argp, CRYPTO_EX_new *new_func, CRYPTO_EX_dup *dup_func, CRYPTO_EX_free *free_func) { -- GitLab