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dtls.c: add callback for peer specific selection of cipher suites.
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Signed-off-by: Achim Kraus <[email protected]>
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@boaks
boaks committed Jun 23, 2022
1 parent fda9206 commit e78c641
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Showing 3 changed files with 113 additions and 33 deletions.
1 change: 1 addition & 0 deletions crypto.h
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Original file line number Diff line number Diff line change
Expand Up @@ -141,6 +141,7 @@ typedef struct {
dtls_hs_state_t hs_state; /**< handshake protocol status */

dtls_compression_t compression; /**< compression method */
const dtls_cipher_t* cipher_suites; /**< list of cipher suites, TLS_NULL_WITH_NULL_NULL terminated */
dtls_cipher_index_t cipher_index; /**< internal index for cipher_suite_params, DTLS_CIPHER_INDEX_NULL for TLS_NULL_WITH_NULL_NULL */
unsigned int do_client_auth:1;
unsigned int extended_master_secret:1;
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133 changes: 100 additions & 33 deletions dtls.c
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Original file line number Diff line number Diff line change
Expand Up @@ -536,6 +536,25 @@ dtls_set_handshake_header(uint8 type,
return buf;
}

static const dtls_cipher_t default_cipher_suites[] =
#ifdef DTLS_DEFAULT_CIPHER_SUITES
DTLS_DEFAULT_CIPHER_SUITES ;
#else
{
#ifdef DTLS_ECC
TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8,
TLS_ECDHE_ECDSA_WITH_AES_128_CCM,
#endif /* DTLS_ECC */
#ifdef DTLS_PSK
TLS_PSK_WITH_AES_128_CCM_8,
TLS_PSK_WITH_AES_128_CCM,
#endif /* DTLS_PSK */
/* TLS_NULL_WITH_NULL_NULL must always be the last entry as it
* indicates the stop marker for the traversal of this table. */
TLS_NULL_WITH_NULL_NULL
};
#endif

/** only one compression method is currently defined */
static uint8 compression_methods[] = {
TLS_COMPRESSION_NULL
Expand Down Expand Up @@ -569,11 +588,22 @@ static const struct cipher_suite_param_t cipher_suite_params[] = {

static const dtls_cipher_index_t last_cipher_suite_param = sizeof(cipher_suite_params) / sizeof(cipher_suite_param_t);

static inline dtls_cipher_index_t get_cipher_index(dtls_cipher_t cipher)
static inline uint8_t contains_cipher_suite(const dtls_cipher_t* cipher_suites, const dtls_cipher_t cipher_suite)
{
while ((*cipher_suites != cipher_suite) &&
(*cipher_suites != TLS_NULL_WITH_NULL_NULL)) {
cipher_suites++;
}
return *cipher_suites == cipher_suite;
}

static inline dtls_cipher_index_t get_cipher_index(const dtls_cipher_t* cipher_suites, dtls_cipher_t cipher)
{
for (int index = 0; index < last_cipher_suite_param ; ++index) {
if (cipher_suite_params[index].cipher_suite == cipher) {
return index;
if (contains_cipher_suite(cipher_suites, cipher)) {
return index;
}
}
}
return DTLS_CIPHER_INDEX_NULL;
Expand Down Expand Up @@ -677,7 +707,7 @@ static inline int is_ecdsa_client_auth_supported(dtls_context_t *ctx)
* @param ctx The current DTLS context
* @param cipher_index The index to cipher suite params to check
* @param is_client 1 for a dtls client, 0 for server
* @return @c 1 iff @p code is recognized,
* @return @c 1 if @p code is recognized,
*/
static int
known_cipher(dtls_context_t *ctx, dtls_cipher_index_t cipher_index, int is_client) {
Expand Down Expand Up @@ -1188,9 +1218,16 @@ dtls_update_parameters(dtls_context_t *ctx,
data += sizeof(uint16);
data_length -= sizeof(uint16) + i;

if (ctx->h->get_cipher_suites != NULL) {
ctx->h->get_cipher_suites(ctx, &peer->session, &config->cipher_suites);
}
if (!config->cipher_suites) {
config->cipher_suites = default_cipher_suites;
}

ok = 0;
while ((i >= (int)sizeof(uint16)) && !ok) {
config->cipher_index = get_cipher_index(dtls_uint16_to_int(data));
config->cipher_index = get_cipher_index(config->cipher_suites, dtls_uint16_to_int(data));
ok = known_cipher(ctx, config->cipher_index, 0);
i -= sizeof(uint16);
data += sizeof(uint16);
Expand All @@ -1202,7 +1239,7 @@ dtls_update_parameters(dtls_context_t *ctx,
if (!ok) {
/* reset config cipher to a well-defined value */
config->cipher_index = DTLS_CIPHER_INDEX_NULL;
dtls_warn("No matching cipher found\n");
dtls_warn("No matching cipher-suite found\n");
goto error;
}

Expand Down Expand Up @@ -2837,21 +2874,21 @@ static int
dtls_send_client_hello(dtls_context_t *ctx, dtls_peer_t *peer,
uint8 cookie[], size_t cookie_length) {
uint8 buf[DTLS_CH_LENGTH_MAX];
uint8 *p = buf;
uint8_t cipher_size;
uint8_t extension_size;
int psk;
int ecdsa;
uint8_t *p = buf;
uint8_t *p_cipher_suites_size = NULL;
uint8_t index = 0;
uint8_t cipher_suites_size = 0;
uint8_t extension_size = 4; /* extended master secret extension */
#ifdef DTLS_ECC
uint8_t ecdsa = 0;
#endif
dtls_handshake_parameters_t *handshake = peer->handshake_params;

psk = is_psk_supported(ctx);
ecdsa = is_ecdsa_supported(ctx, 1);

cipher_size = 2 + ((ecdsa) ? 4 : 0) + ((psk) ? 4 : 0);
extension_size = 4 + ((ecdsa) ? 6 + 6 + 8 + 6 + 8: 0);

if (cipher_size == 0) {
dtls_crit("no cipher callbacks implemented\n");
if (ctx->h->get_cipher_suites != NULL) {
ctx->h->get_cipher_suites(ctx, &peer->session, &(handshake->cipher_suites));
}
if (!handshake->cipher_suites) {
handshake->cipher_suites = default_cipher_suites;
}

dtls_int_to_uint16(p, DTLS_VERSION);
Expand Down Expand Up @@ -2882,22 +2919,47 @@ dtls_send_client_hello(dtls_context_t *ctx, dtls_peer_t *peer,
p += cookie_length;
}

/* add known cipher(s) */
dtls_int_to_uint16(p, cipher_size - 2);
/* keep pointer to size of cipher suites */
p_cipher_suites_size = p;
/* skip size of cipher suites field */
p += sizeof(uint16);

if (ecdsa) {
dtls_int_to_uint16(p, TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8);
p += sizeof(uint16);
dtls_int_to_uint16(p, TLS_ECDHE_ECDSA_WITH_AES_128_CCM);
p += sizeof(uint16);
/* add known cipher(s) */
for (index = 0; handshake->cipher_suites[index] != TLS_NULL_WITH_NULL_NULL; ++index) {
dtls_cipher_t code = handshake->cipher_suites[index];
dtls_cipher_index_t cipher_index = get_cipher_index(handshake->cipher_suites, code);
if (known_cipher(ctx, cipher_index, 1)) {
dtls_int_to_uint16(p, code);
p += sizeof(uint16);
#ifdef DTLS_ECC
ecdsa = ecdsa || is_key_exchange_ecdhe_ecdsa(cipher_index);
#endif /* DTLS_ECC */
}
/* ignore not supported cipher-suite
credentials callback is missing */
}
if (psk) {
dtls_int_to_uint16(p, TLS_PSK_WITH_AES_128_CCM_8);
p += sizeof(uint16);
dtls_int_to_uint16(p, TLS_PSK_WITH_AES_128_CCM);
p += sizeof(uint16);

cipher_suites_size = (p - p_cipher_suites_size) - sizeof(uint16);
if (cipher_suites_size == 0) {
dtls_crit("no supported cipher suite provided!\n");
return dtls_alert_fatal_create(DTLS_ALERT_HANDSHAKE_FAILURE);
}

/* set size of known cipher suites */
dtls_int_to_uint16(p_cipher_suites_size, cipher_suites_size);

#ifdef DTLS_ECC
if (ecdsa) {
/*
* client_cert_type := 6 bytes
* server_cert_type := 6 bytes
* ec curves := 8 bytes
* ec point format := 6 bytes
* sign. and hash algos := 8 bytes
*/
extension_size += 6 + 6 + 8 + 6 + 8;
}
#endif

/* compression method */
dtls_int_to_uint8(p, 1);
Expand All @@ -2910,6 +2972,7 @@ dtls_send_client_hello(dtls_context_t *ctx, dtls_peer_t *peer,
dtls_int_to_uint16(p, extension_size);
p += sizeof(uint16);

#ifdef DTLS_ECC
if (ecdsa) {
/* client certificate type extension */
dtls_int_to_uint16(p, TLS_EXT_CLIENT_CERTIFICATE_TYPE);
Expand Down Expand Up @@ -2992,6 +3055,8 @@ dtls_send_client_hello(dtls_context_t *ctx, dtls_peer_t *peer,
p += sizeof(uint8);

}
#endif /* DTLS_ECC */

/* extended master secret */
dtls_int_to_uint16(p, TLS_EXT_EXTENDED_MASTER_SECRET);
p += sizeof(uint16);
Expand Down Expand Up @@ -3069,12 +3134,14 @@ check_server_hello(dtls_context_t *ctx,
/* Check cipher suite. As we offer all we have, it is sufficient
* to check if the cipher suite selected by the server is in our
* list of known cipher suites. Subsets are not supported. */
handshake->cipher_index = get_cipher_index(dtls_uint16_to_int(data));
handshake->cipher_index = get_cipher_index(handshake->cipher_suites, dtls_uint16_to_int(data));

if (!known_cipher(ctx, handshake->cipher_index, 1)) {
dtls_alert("unsupported cipher 0x%02x 0x%02x\n",
data[0], data[1]);
dtls_alert("unsupported cipher 0x%02x 0x%02x\n", data[0], data[1]);
handshake->cipher_index = DTLS_CIPHER_INDEX_NULL;
return dtls_alert_fatal_create(DTLS_ALERT_INSUFFICIENT_SECURITY);
}

data += sizeof(uint16);
data_length -= sizeof(uint16);

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12 changes: 12 additions & 0 deletions dtls.h
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Original file line number Diff line number Diff line change
Expand Up @@ -119,6 +119,18 @@ typedef struct {
int (*event)(struct dtls_context_t *ctx, session_t *session,
dtls_alert_level_t level, unsigned short code);

/**
* Called during handshake to get the list of cipher suites.
*
* @param ctx The current dtls context.
* @param session The session where the cipher suites will be used.
* @param cipher_suites The pointer to return the list of cipher suites.
* The list must be terminated by TLS_NULL_WITH_NULL_NULL
* If NULL is assigned, the default cipher suites
* will be used.
*/
void (*get_cipher_suites)(struct dtls_context_t *ctx, session_t *session, const dtls_cipher_t **cipher_suites);

#ifdef DTLS_PSK
/**
* Called during handshake to get information related to the
Expand Down

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