Update SPTPS protocol.
* Exchange nonce and ECDH public key first, calculate the ECDSA signature over the complete key exchange. * Make an explicit distinction between client and server in the signatures. * Add more comments and replace some magic numbers by #defines. Thanks to Erik Tews for very helpful hints and comments!
This commit is contained in:
Guus Sliepen
parent
810847248a
commit
3001351150
3 changed files with 157 additions and 59 deletions
1
THANKS
1
THANKS
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@ -9,6 +9,7 @@ We would like to thank the following people for their contributions to tinc:
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* Delf Eldkraft
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* dnk
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* Enrique Zanardi
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* Erik Tews
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* Flynn Marquardt
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* Grzegorz Dymarek
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* Hans Bayle
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198
src/sptps.c
198
src/sptps.c
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@ -30,12 +30,34 @@
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char *logfilename;
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#include "utils.c"
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/*
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Nonce MUST be exchanged first (done)
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Signatures MUST be done over both nonces, to guarantee the signature is fresh
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Otherwise: if ECDHE key of one side is compromised, it can be reused!
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Add explicit tag to beginning of structure to distinguish the client and server when signing. (done)
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Sign all handshake messages up to ECDHE kex with long-term public keys. (done)
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HMACed KEX finished message to prevent downgrade attacks and prove you have the right key material (done by virtue of ECDSA over the whole ECDHE exchange?)
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Explicit close message needs to be added.
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Maybe do add some alert messages to give helpful error messages? Not more than TLS sends.
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Use counter mode instead of OFB.
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Make sure ECC operations are fixed time (aka prevent side-channel attacks).
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*/
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// Log an error message.
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static bool error(sptps_t *s, int s_errno, const char *msg) {
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fprintf(stderr, "SPTPS error: %s\n", msg);
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errno = s_errno;
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return false;
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}
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// Send a record (private version, accepts all record types, handles encryption and authentication).
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static bool send_record_priv(sptps_t *s, uint8_t type, const char *data, uint16_t len) {
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char plaintext[len + 23];
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char ciphertext[len + 19];
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@ -51,7 +73,7 @@ static bool send_record_priv(sptps_t *s, uint8_t type, const char *data, uint16_
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// Add plaintext (TODO: avoid unnecessary copy)
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memcpy(plaintext + 7, data, len);
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if(s->state) {
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if(s->outstate) {
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// If first handshake has finished, encrypt and HMAC
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if(!digest_create(&s->outdigest, plaintext, len + 7, plaintext + 7 + len))
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return false;
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@ -66,46 +88,66 @@ static bool send_record_priv(sptps_t *s, uint8_t type, const char *data, uint16_
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}
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}
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// Send an application record.
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bool send_record(sptps_t *s, uint8_t type, const char *data, uint16_t len) {
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// Sanity checks: application cannot send data before handshake is finished,
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// and only record types 0..127 are allowed.
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if(!s->state)
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if(!s->outstate)
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return error(s, EINVAL, "Handshake phase not finished yet");
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if(type & 128)
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if(type >= SPTPS_HANDSHAKE)
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return error(s, EINVAL, "Invalid application record type");
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return send_record_priv(s, type, data, len);
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}
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// Send a Key EXchange record, containing a random nonce and an ECDHE public key.
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static bool send_kex(sptps_t *s) {
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size_t keylen = ECDH_SIZE;
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size_t siglen = ecdsa_size(&s->mykey);
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char data[32 + keylen + siglen];
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// Create a random nonce.
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s->myrandom = realloc(s->myrandom, 32);
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if(!s->myrandom)
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// Make room for our KEX message, which we will keep around since send_sig() needs it.
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s->mykex = realloc(s->mykex, 1 + 32 + keylen);
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if(!s->mykex)
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return error(s, errno, strerror(errno));
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randomize(s->myrandom, 32);
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memcpy(data, s->myrandom, 32);
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// Set version byte to zero.
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s->mykex[0] = SPTPS_VERSION;
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// Create a random nonce.
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randomize(s->mykex + 1, 32);
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// Create a new ECDH public key.
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if(!ecdh_generate_public(&s->ecdh, data + 32))
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if(!ecdh_generate_public(&s->ecdh, s->mykex + 1 + 32))
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return false;
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// Sign the former.
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if(!ecdsa_sign(&s->mykey, data, 32 + keylen, data + 32 + keylen))
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return false;
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// Send the handshake record.
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return send_record_priv(s, 128, data, sizeof data);
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return send_record_priv(s, SPTPS_HANDSHAKE, s->mykex, 1 + 32 + keylen);
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}
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static bool generate_key_material(sptps_t *s, const char *shared, size_t len, const char *hisrandom) {
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// Send a SIGnature record, containing an ECDSA signature over both KEX records.
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static bool send_sig(sptps_t *s) {
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size_t keylen = ECDH_SIZE;
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size_t siglen = ecdsa_size(&s->mykey);
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// Concatenate both KEX messages, plus tag indicating if it is from the connection originator
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char msg[(1 + 32 + keylen) * 2 + 1];
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char sig[siglen];
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msg[0] = s->initiator;
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memcpy(msg + 1, s->mykex, 1 + 32 + keylen);
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memcpy(msg + 2 + 32 + keylen, s->hiskex, 1 + 32 + keylen);
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// Sign the result.
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if(!ecdsa_sign(&s->mykey, msg, sizeof msg, sig))
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return false;
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// Send the SIG exchange record.
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return send_record_priv(s, SPTPS_HANDSHAKE, sig, sizeof sig);
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}
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// Generate key material from the shared secret created from the ECDHE key exchange.
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static bool generate_key_material(sptps_t *s, const char *shared, size_t len) {
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// Initialise cipher and digest structures if necessary
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if(!s->state) {
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if(!s->outstate) {
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bool result
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= cipher_open_by_name(&s->incipher, "aes-256-ofb")
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&& cipher_open_by_name(&s->outcipher, "aes-256-ofb")
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@ -126,11 +168,11 @@ static bool generate_key_material(sptps_t *s, const char *shared, size_t len, co
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char seed[s->labellen + 64 + 13];
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strcpy(seed, "key expansion");
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if(s->initiator) {
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memcpy(seed + 13, hisrandom, 32);
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memcpy(seed + 45, s->myrandom, 32);
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memcpy(seed + 13, s->mykex + 1, 32);
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memcpy(seed + 45, s->hiskex + 1, 32);
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} else {
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memcpy(seed + 13, s->myrandom, 32);
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memcpy(seed + 45, hisrandom, 32);
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memcpy(seed + 13, s->hiskex + 1, 32);
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memcpy(seed + 45, s->mykex + 1, 32);
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}
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memcpy(seed + 78, s->label, s->labellen);
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@ -141,10 +183,12 @@ static bool generate_key_material(sptps_t *s, const char *shared, size_t len, co
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return true;
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}
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// Send an ACKnowledgement record.
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static bool send_ack(sptps_t *s) {
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return send_record_priv(s, 128, "", 0);
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return send_record_priv(s, SPTPS_HANDSHAKE, "", 0);
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}
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// Receive an ACKnowledgement record.
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static bool receive_ack(sptps_t *s, const char *data, uint16_t len) {
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if(len)
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return false;
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@ -153,33 +197,58 @@ static bool receive_ack(sptps_t *s, const char *data, uint16_t len) {
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return error(s, ENOSYS, "receive_ack() not completely implemented yet");
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}
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// Receive a Key EXchange record, respond by sending a SIG record.
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static bool receive_kex(sptps_t *s, const char *data, uint16_t len) {
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// Verify length of the HELLO record
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if(len != 1 + 32 + ECDH_SIZE)
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return error(s, EIO, "Invalid KEX record length");
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// Ignore version number for now.
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// Make a copy of the KEX message, send_sig() and receive_sig() need it
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s->hiskex = realloc(s->hiskex, len);
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if(!s->hiskex)
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return error(s, errno, strerror(errno));
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memcpy(s->hiskex, data, len);
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return send_sig(s);
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}
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// Receive a SIGnature record, verify it, if it passed, compute the shared secret and calculate the session keys.
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static bool receive_sig(sptps_t *s, const char *data, uint16_t len) {
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size_t keylen = ECDH_SIZE;
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size_t siglen = ecdsa_size(&s->hiskey);
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// Verify length of KEX record.
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if(len != 32 + keylen + siglen)
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if(len != siglen)
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return error(s, EIO, "Invalid KEX record length");
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// Concatenate both KEX messages, plus tag indicating if it is from the connection originator
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char msg[(1 + 32 + keylen) * 2 + 1];
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msg[0] = !s->initiator;
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memcpy(msg + 1, s->hiskex, 1 + 32 + keylen);
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memcpy(msg + 2 + 32 + keylen, s->mykex, 1 + 32 + keylen);
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// Verify signature.
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if(!ecdsa_verify(&s->hiskey, data, 32 + keylen, data + 32 + keylen))
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if(!ecdsa_verify(&s->hiskey, msg, sizeof msg, data))
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return false;
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// Compute shared secret.
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char shared[ECDH_SHARED_SIZE];
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if(!ecdh_compute_shared(&s->ecdh, data + 32, shared))
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if(!ecdh_compute_shared(&s->ecdh, s->hiskex + 1 + 32, shared))
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return false;
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// Generate key material from shared secret.
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if(!generate_key_material(s, shared, sizeof shared, data))
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if(!generate_key_material(s, shared, sizeof shared))
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return false;
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// Send cipher change record if necessary
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if(s->state)
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if(!send_ack(s))
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return false;
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//if(s->outstate && !send_ack(s))
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// return false;
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// TODO: set cipher/digest keys
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// TODO: only set new keys after ACK has been set/received
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if(s->initiator) {
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bool result
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= cipher_set_key(&s->incipher, s->key, false)
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@ -198,39 +267,56 @@ static bool receive_kex(sptps_t *s, const char *data, uint16_t len) {
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return false;
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}
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s->outstate = true;
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s->instate = true;
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return true;
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}
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// Force another Key EXchange (for testing purposes).
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bool force_kex(sptps_t *s) {
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if(!s->outstate || s->state != SPTPS_SECONDARY_KEX)
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return error(s, EINVAL, "Cannot force KEX in current state");
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s->state = SPTPS_KEX;
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return send_kex(s);
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}
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// Receive a handshake record.
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static bool receive_handshake(sptps_t *s, const char *data, uint16_t len) {
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// Only a few states to deal with handshaking.
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fprintf(stderr, "Received handshake message, current state %d\n", s->state);
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switch(s->state) {
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case 0:
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// We have sent our public ECDH key, we expect our peer to sent one as well.
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if(!receive_kex(s, data, len))
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return false;
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s->state = 1;
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return true;
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case 1:
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// We receive a secondary key exchange request, first respond by sending our own public ECDH key.
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case SPTPS_SECONDARY_KEX:
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// We receive a secondary KEX request, first respond by sending our own.
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if(!send_kex(s))
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return false;
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case 2:
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// If we already sent our secondary public ECDH key, we expect the peer to send his.
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case SPTPS_KEX:
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// We have sent our KEX request, we expect our peer to sent one as well.
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if(!receive_kex(s, data, len))
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return false;
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s->state = 3;
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s->state = SPTPS_SIG;
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return true;
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case 3:
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// We expect an empty handshake message to indicate transition to the new keys.
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case SPTPS_SIG:
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// If we already sent our secondary public ECDH key, we expect the peer to send his.
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if(!receive_sig(s, data, len))
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return false;
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// s->state = SPTPS_ACK;
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s->state = SPTPS_SECONDARY_KEX;
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return true;
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case SPTPS_ACK:
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// We expect a handshake message to indicate transition to the new keys.
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if(!receive_ack(s, data, len))
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return false;
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s->state = 1;
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s->state = SPTPS_SECONDARY_KEX;
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return true;
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// TODO: split ACK into a VERify and ACK?
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default:
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return error(s, EIO, "Invalid session state");
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}
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}
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// Receive incoming data. Check if it contains a complete record, if so, handle it.
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bool receive_data(sptps_t *s, const char *data, size_t len) {
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while(len) {
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// First read the 2 length bytes.
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@ -239,7 +325,7 @@ bool receive_data(sptps_t *s, const char *data, size_t len) {
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if(toread > len)
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toread = len;
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if(s->state) {
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if(s->instate) {
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if(!cipher_decrypt(&s->incipher, data, toread, s->inbuf + s->buflen, NULL, false))
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return false;
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} else {
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@ -275,11 +361,11 @@ bool receive_data(sptps_t *s, const char *data, size_t len) {
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uint16_t reclen;
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memcpy(&reclen, s->inbuf + 4, 2);
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reclen = htons(reclen);
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size_t toread = reclen + (s->state ? 23UL : 7UL) - s->buflen;
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size_t toread = reclen + (s->instate ? 23UL : 7UL) - s->buflen;
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if(toread > len)
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toread = len;
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if(s->state) {
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if(s->instate) {
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if(!cipher_decrypt(&s->incipher, data, toread, s->inbuf + s->buflen, NULL, false))
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return false;
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} else {
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@ -291,21 +377,21 @@ bool receive_data(sptps_t *s, const char *data, size_t len) {
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data += toread;
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// If we don't have a whole record, exit.
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if(s->buflen < reclen + (s->state ? 23UL : 7UL))
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if(s->buflen < reclen + (s->instate ? 23UL : 7UL))
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return true;
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// Check HMAC.
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if(s->state)
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if(s->instate)
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if(!digest_verify(&s->indigest, s->inbuf, reclen + 7UL, s->inbuf + reclen + 7UL))
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error(s, EIO, "Invalid HMAC");
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uint8_t type = s->inbuf[6];
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// Handle record.
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if(type < 128) {
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if(type < SPTPS_HANDSHAKE) {
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if(!s->receive_record(s->handle, type, s->inbuf + 7, reclen))
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return false;
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} else if(type == 128) {
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} else if(type == SPTPS_HANDSHAKE) {
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if(!receive_handshake(s, s->inbuf + 7, reclen))
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return false;
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} else {
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@ -318,6 +404,7 @@ bool receive_data(sptps_t *s, const char *data, size_t len) {
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return true;
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}
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// Start a SPTPS session.
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bool start_sptps(sptps_t *s, void *handle, bool initiator, ecdsa_t mykey, ecdsa_t hiskey, const char *label, size_t labellen, send_data_t send_data, receive_record_t receive_record) {
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// Initialise struct sptps
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memset(s, 0, sizeof *s);
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@ -344,14 +431,17 @@ bool start_sptps(sptps_t *s, void *handle, bool initiator, ecdsa_t mykey, ecdsa_
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s->receive_record = receive_record;
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// Do first KEX immediately
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s->state = SPTPS_KEX;
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return send_kex(s);
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}
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// Stop a SPTPS session.
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bool stop_sptps(sptps_t *s) {
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// Clean up any resources.
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ecdh_free(&s->ecdh);
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free(s->inbuf);
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free(s->myrandom);
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free(s->mykex);
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free(s->hiskex);
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free(s->key);
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free(s->label);
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return true;
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17
src/sptps.h
17
src/sptps.h
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@ -24,10 +24,13 @@
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#include "ecdh.h"
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#include "ecdsa.h"
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#define STATE_FIRST_KEX 0 // Waiting for peer's ECDHE pubkey
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#define STATE_NORMAL 1
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#define STATE_WAIT_KEX 2 // Waiting for peer's ECDHE pubkey
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#define STATE_WAIT_ACK 3 // Waiting for peer's acknowledgement of pubkey reception
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#define SPTPS_KEX 0
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#define SPTPS_SECONDARY_KEX 1 // Waiting for peer's ECDHE pubkey
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#define SPTPS_SIG 2 // Waiting for peer's ECDHE pubkey
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#define SPTPS_ACK 3 // Waiting for peer's acknowledgement of pubkey reception
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#define SPTPS_HANDSHAKE 128
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#define SPTPS_VERSION 128
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typedef bool (*send_data_t)(void *handle, const char *data, size_t len);
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typedef bool (*receive_record_t)(void *handle, uint8_t type, const char *data, uint16_t len);
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@ -39,10 +42,12 @@ typedef struct sptps {
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char *inbuf;
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size_t buflen;
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bool instate;
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cipher_t incipher;
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digest_t indigest;
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uint32_t inseqno;
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bool outstate;
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cipher_t outcipher;
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digest_t outdigest;
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uint32_t outseqno;
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||||
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|
@ -51,7 +56,8 @@ typedef struct sptps {
|
|||
ecdsa_t hiskey;
|
||||
ecdh_t ecdh;
|
||||
|
||||
char *myrandom;
|
||||
char *mykex;
|
||||
char *hiskex;
|
||||
char *key;
|
||||
char *label;
|
||||
size_t labellen;
|
||||
|
|
@ -65,3 +71,4 @@ extern bool start_sptps(sptps_t *s, void *handle, bool initiator, ecdsa_t mykey,
|
|||
extern bool stop_sptps(sptps_t *s);
|
||||
extern bool send_record(sptps_t *s, uint8_t type, const char *data, uint16_t len);
|
||||
extern bool receive_data(sptps_t *s, const char *data, size_t len);
|
||||
extern bool force_kex(sptps_t *s);
|
||||
|
|
|
|||
Loading…
Reference in a new issue