char *logfilename;
#include "utils.c"
+/*
+ Nonce MUST be exchanged first (done)
+ Signatures MUST be done over both nonces, to guarantee the signature is fresh
+ Otherwise: if ECDHE key of one side is compromised, it can be reused!
+
+ Add explicit tag to beginning of structure to distinguish the client and server when signing. (done)
+
+ Sign all handshake messages up to ECDHE kex with long-term public keys. (done)
+
+ 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?)
+
+ Explicit close message needs to be added.
+
+ Maybe do add some alert messages to give helpful error messages? Not more than TLS sends.
+
+ Use counter mode instead of OFB.
+
+ Make sure ECC operations are fixed time (aka prevent side-channel attacks).
+*/
+
+// Log an error message.
static bool error(sptps_t *s, int s_errno, const char *msg) {
fprintf(stderr, "SPTPS error: %s\n", msg);
errno = s_errno;
return false;
}
+// Send a record (private version, accepts all record types, handles encryption and authentication).
static bool send_record_priv(sptps_t *s, uint8_t type, const char *data, uint16_t len) {
char plaintext[len + 23];
char ciphertext[len + 19];
// Add plaintext (TODO: avoid unnecessary copy)
memcpy(plaintext + 7, data, len);
- if(s->state) {
+ if(s->outstate) {
// If first handshake has finished, encrypt and HMAC
if(!digest_create(&s->outdigest, plaintext, len + 7, plaintext + 7 + len))
return false;
}
}
+// Send an application record.
bool send_record(sptps_t *s, uint8_t type, const char *data, uint16_t len) {
// Sanity checks: application cannot send data before handshake is finished,
// and only record types 0..127 are allowed.
- if(!s->state)
+ if(!s->outstate)
return error(s, EINVAL, "Handshake phase not finished yet");
- if(type & 128)
+ if(type >= SPTPS_HANDSHAKE)
return error(s, EINVAL, "Invalid application record type");
return send_record_priv(s, type, data, len);
}
+// Send a Key EXchange record, containing a random nonce and an ECDHE public key.
static bool send_kex(sptps_t *s) {
size_t keylen = ECDH_SIZE;
- size_t siglen = ecdsa_size(&s->mykey);
- char data[32 + keylen + siglen];
- // Create a random nonce.
- s->myrandom = realloc(s->myrandom, 32);
- if(!s->myrandom)
+ // Make room for our KEX message, which we will keep around since send_sig() needs it.
+ s->mykex = realloc(s->mykex, 1 + 32 + keylen);
+ if(!s->mykex)
return error(s, errno, strerror(errno));
- randomize(s->myrandom, 32);
- memcpy(data, s->myrandom, 32);
+ // Set version byte to zero.
+ s->mykex[0] = SPTPS_VERSION;
+
+ // Create a random nonce.
+ randomize(s->mykex + 1, 32);
// Create a new ECDH public key.
- if(!ecdh_generate_public(&s->ecdh, data + 32))
+ if(!ecdh_generate_public(&s->ecdh, s->mykex + 1 + 32))
return false;
- // Sign the former.
- if(!ecdsa_sign(&s->mykey, data, 32 + keylen, data + 32 + keylen))
+ return send_record_priv(s, SPTPS_HANDSHAKE, s->mykex, 1 + 32 + keylen);
+}
+
+// Send a SIGnature record, containing an ECDSA signature over both KEX records.
+static bool send_sig(sptps_t *s) {
+ size_t keylen = ECDH_SIZE;
+ size_t siglen = ecdsa_size(&s->mykey);
+
+ // Concatenate both KEX messages, plus tag indicating if it is from the connection originator
+ char msg[(1 + 32 + keylen) * 2 + 1];
+ char sig[siglen];
+
+ msg[0] = s->initiator;
+ memcpy(msg + 1, s->mykex, 1 + 32 + keylen);
+ memcpy(msg + 2 + 32 + keylen, s->hiskex, 1 + 32 + keylen);
+
+ // Sign the result.
+ if(!ecdsa_sign(&s->mykey, msg, sizeof msg, sig))
return false;
- // Send the handshake record.
- return send_record_priv(s, 128, data, sizeof data);
+ // Send the SIG exchange record.
+ return send_record_priv(s, SPTPS_HANDSHAKE, sig, sizeof sig);
}
-static bool generate_key_material(sptps_t *s, const char *shared, size_t len, const char *hisrandom) {
+// Generate key material from the shared secret created from the ECDHE key exchange.
+static bool generate_key_material(sptps_t *s, const char *shared, size_t len) {
// Initialise cipher and digest structures if necessary
- if(!s->state) {
+ if(!s->outstate) {
bool result
= cipher_open_by_name(&s->incipher, "aes-256-ofb")
&& cipher_open_by_name(&s->outcipher, "aes-256-ofb")
char seed[s->labellen + 64 + 13];
strcpy(seed, "key expansion");
if(s->initiator) {
- memcpy(seed + 13, hisrandom, 32);
- memcpy(seed + 45, s->myrandom, 32);
+ memcpy(seed + 13, s->mykex + 1, 32);
+ memcpy(seed + 45, s->hiskex + 1, 32);
} else {
- memcpy(seed + 13, s->myrandom, 32);
- memcpy(seed + 45, hisrandom, 32);
+ memcpy(seed + 13, s->hiskex + 1, 32);
+ memcpy(seed + 45, s->mykex + 1, 32);
}
memcpy(seed + 78, s->label, s->labellen);
return true;
}
+// Send an ACKnowledgement record.
static bool send_ack(sptps_t *s) {
- return send_record_priv(s, 128, "", 0);
+ return send_record_priv(s, SPTPS_HANDSHAKE, "", 0);
}
+// Receive an ACKnowledgement record.
static bool receive_ack(sptps_t *s, const char *data, uint16_t len) {
if(len)
return false;
return error(s, ENOSYS, "receive_ack() not completely implemented yet");
}
+// Receive a Key EXchange record, respond by sending a SIG record.
static bool receive_kex(sptps_t *s, const char *data, uint16_t len) {
+ // Verify length of the HELLO record
+ if(len != 1 + 32 + ECDH_SIZE)
+ return error(s, EIO, "Invalid KEX record length");
+
+ // Ignore version number for now.
+
+ // Make a copy of the KEX message, send_sig() and receive_sig() need it
+ s->hiskex = realloc(s->hiskex, len);
+ if(!s->hiskex)
+ return error(s, errno, strerror(errno));
+
+ memcpy(s->hiskex, data, len);
+
+ return send_sig(s);
+}
+
+// Receive a SIGnature record, verify it, if it passed, compute the shared secret and calculate the session keys.
+static bool receive_sig(sptps_t *s, const char *data, uint16_t len) {
size_t keylen = ECDH_SIZE;
size_t siglen = ecdsa_size(&s->hiskey);
// Verify length of KEX record.
- if(len != 32 + keylen + siglen)
+ if(len != siglen)
return error(s, EIO, "Invalid KEX record length");
+ // Concatenate both KEX messages, plus tag indicating if it is from the connection originator
+ char msg[(1 + 32 + keylen) * 2 + 1];
+
+ msg[0] = !s->initiator;
+ memcpy(msg + 1, s->hiskex, 1 + 32 + keylen);
+ memcpy(msg + 2 + 32 + keylen, s->mykex, 1 + 32 + keylen);
+
// Verify signature.
- if(!ecdsa_verify(&s->hiskey, data, 32 + keylen, data + 32 + keylen))
+ if(!ecdsa_verify(&s->hiskey, msg, sizeof msg, data))
return false;
// Compute shared secret.
char shared[ECDH_SHARED_SIZE];
- if(!ecdh_compute_shared(&s->ecdh, data + 32, shared))
+ if(!ecdh_compute_shared(&s->ecdh, s->hiskex + 1 + 32, shared))
return false;
// Generate key material from shared secret.
- if(!generate_key_material(s, shared, sizeof shared, data))
+ if(!generate_key_material(s, shared, sizeof shared))
return false;
// Send cipher change record if necessary
- if(s->state)
- if(!send_ack(s))
- return false;
+ //if(s->outstate && !send_ack(s))
+ // return false;
- // TODO: set cipher/digest keys
+ // TODO: only set new keys after ACK has been set/received
if(s->initiator) {
bool result
= cipher_set_key(&s->incipher, s->key, false)
return false;
}
+ s->outstate = true;
+ s->instate = true;
+
return true;
}
+// Force another Key EXchange (for testing purposes).
+bool force_kex(sptps_t *s) {
+ if(!s->outstate || s->state != SPTPS_SECONDARY_KEX)
+ return error(s, EINVAL, "Cannot force KEX in current state");
+
+ s->state = SPTPS_KEX;
+ return send_kex(s);
+}
+
+// Receive a handshake record.
static bool receive_handshake(sptps_t *s, const char *data, uint16_t len) {
// Only a few states to deal with handshaking.
+ fprintf(stderr, "Received handshake message, current state %d\n", s->state);
switch(s->state) {
- case 0:
- // We have sent our public ECDH key, we expect our peer to sent one as well.
+ case SPTPS_SECONDARY_KEX:
+ // We receive a secondary KEX request, first respond by sending our own.
+ if(!send_kex(s))
+ return false;
+ case SPTPS_KEX:
+ // We have sent our KEX request, we expect our peer to sent one as well.
if(!receive_kex(s, data, len))
return false;
- s->state = 1;
+ s->state = SPTPS_SIG;
return true;
- case 1:
- // We receive a secondary key exchange request, first respond by sending our own public ECDH key.
- if(!send_kex(s))
- return false;
- case 2:
+ case SPTPS_SIG:
// If we already sent our secondary public ECDH key, we expect the peer to send his.
- if(!receive_kex(s, data, len))
+ if(!receive_sig(s, data, len))
return false;
- s->state = 3;
+ // s->state = SPTPS_ACK;
+ s->state = SPTPS_SECONDARY_KEX;
return true;
- case 3:
- // We expect an empty handshake message to indicate transition to the new keys.
+ case SPTPS_ACK:
+ // We expect a handshake message to indicate transition to the new keys.
if(!receive_ack(s, data, len))
return false;
- s->state = 1;
+ s->state = SPTPS_SECONDARY_KEX;
return true;
+ // TODO: split ACK into a VERify and ACK?
default:
return error(s, EIO, "Invalid session state");
}
}
+// Receive incoming data. Check if it contains a complete record, if so, handle it.
bool receive_data(sptps_t *s, const char *data, size_t len) {
while(len) {
// First read the 2 length bytes.
if(toread > len)
toread = len;
- if(s->state) {
+ if(s->instate) {
if(!cipher_decrypt(&s->incipher, data, toread, s->inbuf + s->buflen, NULL, false))
return false;
} else {
uint16_t reclen;
memcpy(&reclen, s->inbuf + 4, 2);
reclen = htons(reclen);
- size_t toread = reclen + (s->state ? 23UL : 7UL) - s->buflen;
+ size_t toread = reclen + (s->instate ? 23UL : 7UL) - s->buflen;
if(toread > len)
toread = len;
- if(s->state) {
+ if(s->instate) {
if(!cipher_decrypt(&s->incipher, data, toread, s->inbuf + s->buflen, NULL, false))
return false;
} else {
data += toread;
// If we don't have a whole record, exit.
- if(s->buflen < reclen + (s->state ? 23UL : 7UL))
+ if(s->buflen < reclen + (s->instate ? 23UL : 7UL))
return true;
// Check HMAC.
- if(s->state)
+ if(s->instate)
if(!digest_verify(&s->indigest, s->inbuf, reclen + 7UL, s->inbuf + reclen + 7UL))
error(s, EIO, "Invalid HMAC");
uint8_t type = s->inbuf[6];
// Handle record.
- if(type < 128) {
+ if(type < SPTPS_HANDSHAKE) {
if(!s->receive_record(s->handle, type, s->inbuf + 7, reclen))
return false;
- } else if(type == 128) {
+ } else if(type == SPTPS_HANDSHAKE) {
if(!receive_handshake(s, s->inbuf + 7, reclen))
return false;
} else {
return true;
}
+// Start a SPTPS session.
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) {
// Initialise struct sptps
memset(s, 0, sizeof *s);
s->receive_record = receive_record;
// Do first KEX immediately
+ s->state = SPTPS_KEX;
return send_kex(s);
}
+// Stop a SPTPS session.
bool stop_sptps(sptps_t *s) {
// Clean up any resources.
ecdh_free(&s->ecdh);
free(s->inbuf);
- free(s->myrandom);
+ free(s->mykex);
+ free(s->hiskex);
free(s->key);
free(s->label);
return true;
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