laforge has submitted this change. ( https://gerrit.osmocom.org/c/osmo-tetra/+/34001 )
Change subject: Added functions that prepare for decryption ......................................................................
Added functions that prepare for decryption
Added functions that will eventually allow for mac resource decryption, voice/traffic decryption and identity decryption. Calls to the true TEA keystream generator functions and TA61 identity decryption function will need to be added in a later patch.
Change-Id: I4e6147f206ad6046f32e08015ec9721b64382ca1 --- M src/crypto/tetra_crypto.c M src/crypto/tetra_crypto.h 2 files changed, 131 insertions(+), 13 deletions(-)
Approvals: laforge: Looks good to me, approved; Verified
diff --git a/src/crypto/tetra_crypto.c b/src/crypto/tetra_crypto.c index 9515a25..d7df293 100644 --- a/src/crypto/tetra_crypto.c +++ b/src/crypto/tetra_crypto.c @@ -150,19 +150,123 @@ return ((tm->tn - 1) | (tm->fn << 2) | (tm->mn << 7) | ((hn & 0x7FFF) << 13) | (dir << 28)); }
-int decrypt_identity(struct tetra_crypto_state *tcs, struct tetra_addr *addr) +static bool generate_keystream(struct tetra_crypto_state *tcs, struct tetra_key *key, struct tetra_tdma_time *t, int num_bits, uint8_t *ks_out) { - return 0; + if (!key) + return false; + + /* Construct IV and prepare buf for bytewise keystream */ + int num_bytes = (num_bits + 7) / 8; + uint8_t ks_bytes[num_bytes]; + uint32_t iv = tea_build_iv(t, tcs->hn, 0); + + /* Compute ECK from net info and CK */ + if (tcs->cn < 0 || tcs->la < 0 || tcs->cc < 0) + /* Missing data for TB5 */ + return false; + + uint8_t eck[10]; + uint8_t cn[2] = {(tcs->cn >> 8) & 0xFF, tcs->cn & 0xFF}; + uint8_t la[2] = {(tcs->la >> 8) & 0xFF, tcs->la & 0xFF}; + uint8_t cc[1] = {tcs->cc & 0xFF}; + /* TODO FIXME add call to TB5 to derive eck */ + + /* Generate keystream with required KSG */ + switch (key->network_info->ksg_type) { + /* TODO FIXME add cases/calls to TEA keystream generator functions */ + default: + fprintf(stderr, "tetra_crypto: KSG type %d not supported\n", key->network_info->ksg_type); + return false; + } + + for (int i = 0; i < num_bytes; i++) + for (int j = 0; j < 8; j++) + ks_out[i * 8 + j] = (ks_bytes[i] >> (7-j)) & 1; + + /* Expand keystream bytes into ubit format */ + for (int i = 0; i < num_bits; i++) + ks_out[i] = (ks_bytes[num_bits / 8] >> (7-(num_bits % 8))) & 1; + + return true; }
-int decrypt_mac_element(struct tetra_crypto_state *tcs, struct tetra_tmvsap_prim *tmvp, struct tetra_key *key, int l1_len, int tmpdu_offset) +bool decrypt_identity(struct tetra_crypto_state *tcs, struct tetra_addr *addr) { - return 0; + /* TODO FIXME implement TA61 decryption */ + return false; }
-int decrypt_voice_timeslot(struct tetra_crypto_state *tcs, struct tetra_tdma_time *tdma_time, int16_t *type1_block) +bool decrypt_mac_element(struct tetra_crypto_state *tcs, struct tetra_tmvsap_prim *tmvp, struct tetra_key *key, int l1_len, int tmpdu_offset) { - return 0; + if (!key || l1_len - tmpdu_offset <= 0) + return false; + + if (tcs->cn < 0 || tcs->la < 0 || tcs->cc < 0) { + printf("tetra_crypto: can't compute TB5 due to incomplete network info (carr %d la %d cc %d)\n", + tcs->cn, tcs->la, tcs->cc); + return false; + } + + struct tetra_tdma_time *tdma_time = &tmvp->u.unitdata.tdma_time; + + /* Compute keystream offset to apply */ + /* TODO FIXME maybe we can rework channel type setting in lower mac, and + avoid using TETRA_LC_UNKNOWN below */ + uint32_t ks_skip_bits = 0; + if (tmvp->u.unitdata.blk_num == BLK_2 && ( + tmvp->u.unitdata.lchan == TETRA_LC_SCH_HD || + tmvp->u.unitdata.lchan == TETRA_LC_UNKNOWN)) { + ks_skip_bits = 216; + printf("tetra_crypto: 2nd half slot; skipping bits\n"); + } + + /* Generate keystream */ + struct msgb *msg = tmvp->oph.msg; + int ct_len = l1_len - tmpdu_offset; + int ks_num_bits = ks_skip_bits + ct_len; + uint8_t *ct_start = msg->l1h + tmpdu_offset; + uint8_t ks[ks_num_bits]; + if (!generate_keystream(tcs, key, tdma_time, ks_num_bits, ks)) + return false; + + /* Apply keystream */ + for (int i = 0; i < ct_len; i++) + ct_start[i] = ct_start[i] ^ ks[i + ks_skip_bits]; + + printf("tetra_crypto: addr %8d -> key %4d, time %5d/%s, tmpdu offset %d, decrypting %d bits\n", + key->addr, key->index, tcs->hn, tetra_tdma_time_dump(tdma_time), tmpdu_offset, ct_len); + + return true; +} + +bool decrypt_voice_timeslot(struct tetra_crypto_state *tcs, struct tetra_tdma_time *tdma_time, int16_t *type1_block) +{ + /* TODO FIXME implement proper key selection for voice blocks */ + struct tetra_key *key = tcs->cck; + if (!key) + return false; + + if (tcs->cn < 0 || tcs->la < 0 || tcs->cc < 0) { + printf("tetra_crypto: can't compute TB5 due to incomplete network info (carr %d la %d cc %d)\n", + tcs->cn, tcs->la, tcs->cc); + return false; + } + + /* Generate keystream */ + int ks_num_bits = 137*2; // two half slots of voice + uint8_t ks[ks_num_bits]; + if (!generate_keystream(tcs, key, tdma_time, ks_num_bits, ks)) + return false; + + /* Apply keystream */ + for (int i = 0; i < 137; i++) { + type1_block[i + 1] = type1_block[i + 1] ^ ks[i]; + type1_block[i + 139] = type1_block[i + 139] ^ ks[i + 137]; + } + + printf("tetra_crypto: addr %8d -> key %4d, time %5d/%s, decrypted voice\n", + key->addr, key->index, tcs->hn, tetra_tdma_time_dump(tdma_time)); + return true; }
int load_keystore(char *tetra_keyfile) @@ -197,7 +301,7 @@ while (fgets(buf, sizeof(buf), fp)) {
if (strlen(buf) <= 1 || buf[0] == '#') { - // Commented/empty line + /* Commented/empty line */ continue;
} else if (!strncmp(buf, "network ", 8)) { @@ -299,11 +403,11 @@
void update_current_network(struct tetra_crypto_state *tcs, int mcc, int mnc) { - // Update globals + /* Update globals */ tcs->mcc = mcc; tcs->mnc = mnc;
- // Network changed, update reference to current network + /* Network changed, update reference to current network */ tcs->network = 0; for (int i = 0; i < tcdb->num_nets; i++) { struct tetra_netinfo *network = &tcdb->nets[i]; @@ -313,7 +417,7 @@ } }
- // (Try to) select new CCK/SCK + /* (Try to) select new CCK/SCK */ update_current_cck(tcs); }
diff --git a/src/crypto/tetra_crypto.h b/src/crypto/tetra_crypto.h index e50a45e..ace4c04 100644 --- a/src/crypto/tetra_crypto.h +++ b/src/crypto/tetra_crypto.h @@ -111,9 +111,9 @@
/* Keystream generation and decryption functions */ uint32_t tea_build_iv(struct tetra_tdma_time *tm, uint16_t hn, uint8_t dir); -int decrypt_identity(struct tetra_crypto_state *tcs, struct tetra_addr *addr); -int decrypt_mac_element(struct tetra_crypto_state *tcs, struct tetra_tmvsap_prim *tmvp, struct tetra_key *key, int l1_len, int tmpdu_offset); -int decrypt_voice_timeslot(struct tetra_crypto_state *tcs, struct tetra_tdma_time *tdma_time, int16_t *type1_bits); +bool decrypt_identity(struct tetra_crypto_state *tcs, struct tetra_addr *addr); +bool decrypt_mac_element(struct tetra_crypto_state *tcs, struct tetra_tmvsap_prim *tmvp, struct tetra_key *key, int l1_len, int tmpdu_offset); +bool decrypt_voice_timeslot(struct tetra_crypto_state *tcs, struct tetra_tdma_time *tdma_time, int16_t *type1_bits);
/* Key selection and crypto state management */ struct tetra_netinfo *get_network_info(int mcc, int mnc);
-
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