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Diffstat (limited to 'src/or/onion_ntor.c')
| -rw-r--r-- | src/or/onion_ntor.c | 300 |
1 files changed, 300 insertions, 0 deletions
diff --git a/src/or/onion_ntor.c b/src/or/onion_ntor.c new file mode 100644 index 000000000..ef501f69d --- /dev/null +++ b/src/or/onion_ntor.c @@ -0,0 +1,300 @@ +/* Copyright (c) 2012-2013, The Tor Project, Inc. */ +/* See LICENSE for licensing information */ + +#include "orconfig.h" + +#include "crypto.h" +#define ONION_NTOR_PRIVATE +#include "onion_ntor.h" +#include "torlog.h" +#include "util.h" + +/** Free storage held in an ntor handshake state. */ +void +ntor_handshake_state_free(ntor_handshake_state_t *state) +{ + if (!state) + return; + memwipe(state, 0, sizeof(*state)); + tor_free(state); +} + +/** Convenience function to represent HMAC_SHA256 as our instantiation of + * ntor's "tweaked hash'. Hash the <b>inp_len</b> bytes at <b>inp</b> into + * a DIGEST256_LEN-byte digest at <b>out</b>, with the hash changing + * depending on the value of <b>tweak</b>. */ +static void +h_tweak(uint8_t *out, + const uint8_t *inp, size_t inp_len, + const char *tweak) +{ + size_t tweak_len = strlen(tweak); + crypto_hmac_sha256((char*)out, tweak, tweak_len, (const char*)inp, inp_len); +} + +/** Wrapper around a set of tweak-values for use with the ntor handshake. */ +typedef struct tweakset_t { + const char *t_mac; + const char *t_key; + const char *t_verify; + const char *m_expand; +} tweakset_t; + +/** The tweaks to be used with our handshake. */ +const tweakset_t proto1_tweaks = { +#define PROTOID "ntor-curve25519-sha256-1" +#define PROTOID_LEN 24 + PROTOID ":mac", + PROTOID ":key_extract", + PROTOID ":verify", + PROTOID ":key_expand" +}; + +/** Convenience macro: copy <b>len</b> bytes from <b>inp</b> to <b>ptr</b>, + * and advance <b>ptr</b> by the number of bytes copied. */ +#define APPEND(ptr, inp, len) \ + STMT_BEGIN { \ + memcpy(ptr, (inp), (len)); \ + ptr += len; \ + } STMT_END + +/** + * Compute the first client-side step of the ntor handshake for communicating + * with a server whose DIGEST_LEN-byte server identity is <b>router_id</b>, + * and whose onion key is <b>router_key</b>. Store the NTOR_ONIONSKIN_LEN-byte + * message in <b>onion_skin_out</b>, and store the handshake state in + * *<b>handshake_state_out</b>. Return 0 on success, -1 on failure. + */ +int +onion_skin_ntor_create(const uint8_t *router_id, + const curve25519_public_key_t *router_key, + ntor_handshake_state_t **handshake_state_out, + uint8_t *onion_skin_out) +{ + ntor_handshake_state_t *state; + uint8_t *op; + + state = tor_malloc_zero(sizeof(ntor_handshake_state_t)); + + memcpy(state->router_id, router_id, DIGEST_LEN); + memcpy(&state->pubkey_B, router_key, sizeof(curve25519_public_key_t)); + if (curve25519_secret_key_generate(&state->seckey_x, 0) < 0) { + tor_free(state); + return -1; + } + curve25519_public_key_generate(&state->pubkey_X, &state->seckey_x); + + op = onion_skin_out; + APPEND(op, router_id, DIGEST_LEN); + APPEND(op, router_key->public_key, CURVE25519_PUBKEY_LEN); + APPEND(op, state->pubkey_X.public_key, CURVE25519_PUBKEY_LEN); + tor_assert(op == onion_skin_out + NTOR_ONIONSKIN_LEN); + + *handshake_state_out = state; + + return 0; +} + +#define SERVER_STR "Server" +#define SERVER_STR_LEN 6 + +#define SECRET_INPUT_LEN (CURVE25519_PUBKEY_LEN * 3 + \ + CURVE25519_OUTPUT_LEN * 2 + \ + DIGEST_LEN + PROTOID_LEN) +#define AUTH_INPUT_LEN (DIGEST256_LEN + DIGEST_LEN + \ + CURVE25519_PUBKEY_LEN*3 + \ + PROTOID_LEN + SERVER_STR_LEN) + +/** + * Perform the server side of an ntor handshake. Given an + * NTOR_ONIONSKIN_LEN-byte message in <b>onion_skin</b>, our own identity + * fingerprint as <b>my_node_id</b>, and an associative array mapping public + * onion keys to curve25519_keypair_t in <b>private_keys</b>, attempt to + * perform the handshake. Use <b>junk_keys</b> if present if the handshake + * indicates an unrecognized public key. Write an NTOR_REPLY_LEN-byte + * message to send back to the client into <b>handshake_reply_out</b>, and + * generate <b>key_out_len</b> bytes of key material in <b>key_out</b>. Return + * 0 on success, -1 on failure. + */ +int +onion_skin_ntor_server_handshake(const uint8_t *onion_skin, + const di_digest256_map_t *private_keys, + const curve25519_keypair_t *junk_keys, + const uint8_t *my_node_id, + uint8_t *handshake_reply_out, + uint8_t *key_out, + size_t key_out_len) +{ + const tweakset_t *T = &proto1_tweaks; + /* Sensitive stack-allocated material. Kept in an anonymous struct to make + * it easy to wipe. */ + struct { + uint8_t secret_input[SECRET_INPUT_LEN]; + uint8_t auth_input[AUTH_INPUT_LEN]; + curve25519_public_key_t pubkey_X; + curve25519_secret_key_t seckey_y; + curve25519_public_key_t pubkey_Y; + uint8_t verify[DIGEST256_LEN]; + } s; + uint8_t *si = s.secret_input, *ai = s.auth_input; + const curve25519_keypair_t *keypair_bB; + int bad; + + /* Decode the onion skin */ + /* XXXX Does this possible early-return business threaten our security? */ + if (tor_memneq(onion_skin, my_node_id, DIGEST_LEN)) + return -1; + /* Note that on key-not-found, we go through with this operation anyway, + * using "junk_keys". This will result in failed authentication, but won't + * leak whether we recognized the key. */ + keypair_bB = dimap_search(private_keys, onion_skin + DIGEST_LEN, + (void*)junk_keys); + if (!keypair_bB) + return -1; + + memcpy(s.pubkey_X.public_key, onion_skin+DIGEST_LEN+DIGEST256_LEN, + CURVE25519_PUBKEY_LEN); + + /* Make y, Y */ + curve25519_secret_key_generate(&s.seckey_y, 0); + curve25519_public_key_generate(&s.pubkey_Y, &s.seckey_y); + + /* NOTE: If we ever use a group other than curve25519, or a different + * representation for its points, we may need to perform different or + * additional checks on X here and on Y in the client handshake, or lose our + * security properties. What checks we need would depend on the properties + * of the group and its representation. + * + * In short: if you use anything other than curve25519, this aspect of the + * code will need to be reconsidered carefully. */ + + /* build secret_input */ + curve25519_handshake(si, &s.seckey_y, &s.pubkey_X); + bad = safe_mem_is_zero(si, CURVE25519_OUTPUT_LEN); + si += CURVE25519_OUTPUT_LEN; + curve25519_handshake(si, &keypair_bB->seckey, &s.pubkey_X); + bad |= safe_mem_is_zero(si, CURVE25519_OUTPUT_LEN); + si += CURVE25519_OUTPUT_LEN; + + APPEND(si, my_node_id, DIGEST_LEN); + APPEND(si, keypair_bB->pubkey.public_key, CURVE25519_PUBKEY_LEN); + APPEND(si, s.pubkey_X.public_key, CURVE25519_PUBKEY_LEN); + APPEND(si, s.pubkey_Y.public_key, CURVE25519_PUBKEY_LEN); + APPEND(si, PROTOID, PROTOID_LEN); + tor_assert(si == s.secret_input + sizeof(s.secret_input)); + + /* Compute hashes of secret_input */ + h_tweak(s.verify, s.secret_input, sizeof(s.secret_input), T->t_verify); + + /* Compute auth_input */ + APPEND(ai, s.verify, DIGEST256_LEN); + APPEND(ai, my_node_id, DIGEST_LEN); + APPEND(ai, keypair_bB->pubkey.public_key, CURVE25519_PUBKEY_LEN); + APPEND(ai, s.pubkey_Y.public_key, CURVE25519_PUBKEY_LEN); + APPEND(ai, s.pubkey_X.public_key, CURVE25519_PUBKEY_LEN); + APPEND(ai, PROTOID, PROTOID_LEN); + APPEND(ai, SERVER_STR, SERVER_STR_LEN); + tor_assert(ai == s.auth_input + sizeof(s.auth_input)); + + /* Build the reply */ + memcpy(handshake_reply_out, s.pubkey_Y.public_key, CURVE25519_PUBKEY_LEN); + h_tweak(handshake_reply_out+CURVE25519_PUBKEY_LEN, + s.auth_input, sizeof(s.auth_input), + T->t_mac); + + /* Generate the key material */ + crypto_expand_key_material_rfc5869_sha256( + s.secret_input, sizeof(s.secret_input), + (const uint8_t*)T->t_key, strlen(T->t_key), + (const uint8_t*)T->m_expand, strlen(T->m_expand), + key_out, key_out_len); + + /* Wipe all of our local state */ + memwipe(&s, 0, sizeof(s)); + + return bad ? -1 : 0; +} + +/** + * Perform the final client side of the ntor handshake, using the state in + * <b>handshake_state</b> and the server's NTOR_REPLY_LEN-byte reply in + * <b>handshake_reply</b>. Generate <b>key_out_len</b> bytes of key material + * in <b>key_out</b>. Return 0 on success, -1 on failure. + */ +int +onion_skin_ntor_client_handshake( + const ntor_handshake_state_t *handshake_state, + const uint8_t *handshake_reply, + uint8_t *key_out, + size_t key_out_len) +{ + const tweakset_t *T = &proto1_tweaks; + /* Sensitive stack-allocated material. Kept in an anonymous struct to make + * it easy to wipe. */ + struct { + curve25519_public_key_t pubkey_Y; + uint8_t secret_input[SECRET_INPUT_LEN]; + uint8_t verify[DIGEST256_LEN]; + uint8_t auth_input[AUTH_INPUT_LEN]; + uint8_t auth[DIGEST256_LEN]; + } s; + uint8_t *ai = s.auth_input, *si = s.secret_input; + const uint8_t *auth_candidate; + int bad; + + /* Decode input */ + memcpy(s.pubkey_Y.public_key, handshake_reply, CURVE25519_PUBKEY_LEN); + auth_candidate = handshake_reply + CURVE25519_PUBKEY_LEN; + + /* See note in server_handshake above about checking points. The + * circumstances under which we'd need to check Y for membership are + * different than those under which we'd be checking X. */ + + /* Compute secret_input */ + curve25519_handshake(si, &handshake_state->seckey_x, &s.pubkey_Y); + bad = safe_mem_is_zero(si, CURVE25519_OUTPUT_LEN); + si += CURVE25519_OUTPUT_LEN; + curve25519_handshake(si, &handshake_state->seckey_x, + &handshake_state->pubkey_B); + bad |= (safe_mem_is_zero(si, CURVE25519_OUTPUT_LEN) << 1); + si += CURVE25519_OUTPUT_LEN; + APPEND(si, handshake_state->router_id, DIGEST_LEN); + APPEND(si, handshake_state->pubkey_B.public_key, CURVE25519_PUBKEY_LEN); + APPEND(si, handshake_state->pubkey_X.public_key, CURVE25519_PUBKEY_LEN); + APPEND(si, s.pubkey_Y.public_key, CURVE25519_PUBKEY_LEN); + APPEND(si, PROTOID, PROTOID_LEN); + tor_assert(si == s.secret_input + sizeof(s.secret_input)); + + /* Compute verify from secret_input */ + h_tweak(s.verify, s.secret_input, sizeof(s.secret_input), T->t_verify); + + /* Compute auth_input */ + APPEND(ai, s.verify, DIGEST256_LEN); + APPEND(ai, handshake_state->router_id, DIGEST_LEN); + APPEND(ai, handshake_state->pubkey_B.public_key, CURVE25519_PUBKEY_LEN); + APPEND(ai, s.pubkey_Y.public_key, CURVE25519_PUBKEY_LEN); + APPEND(ai, handshake_state->pubkey_X.public_key, CURVE25519_PUBKEY_LEN); + APPEND(ai, PROTOID, PROTOID_LEN); + APPEND(ai, SERVER_STR, SERVER_STR_LEN); + tor_assert(ai == s.auth_input + sizeof(s.auth_input)); + + /* Compute auth */ + h_tweak(s.auth, s.auth_input, sizeof(s.auth_input), T->t_mac); + + bad |= (tor_memneq(s.auth, auth_candidate, DIGEST256_LEN) << 2); + + crypto_expand_key_material_rfc5869_sha256( + s.secret_input, sizeof(s.secret_input), + (const uint8_t*)T->t_key, strlen(T->t_key), + (const uint8_t*)T->m_expand, strlen(T->m_expand), + key_out, key_out_len); + + memwipe(&s, 0, sizeof(s)); + + if (bad) { + log_warn(LD_PROTOCOL, "Invalid result from curve25519 handshake: %d", bad); + } + + return bad ? -1 : 0; +} + |