From 8884fd8bbde92c3d9f4427b00e3c08fbe629f5bf Mon Sep 17 00:00:00 2001 From: Tim Kourt Date: Thu, 12 Dec 2019 12:10:16 -0800 Subject: [PATCH] peap: Add support for Crypto-Binding in PEAPv0 The Crypto Binding TLV is used to ensure that the EAP peer and the EAP server participated in both the inner and the outer EAP authentications of a PEAP authentication by cryptographically associating the phase 1 and phase 2 authentications. The usage of Crypto-Binding in PEAPv0 is optional and is triggered by the reception of the Crypto-Binding TLV from the server. --- src/eap-peap.c | 170 ++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 169 insertions(+), 1 deletion(-) diff --git a/src/eap-peap.c b/src/eap-peap.c index 8059e60b..5de6e862 100644 --- a/src/eap-peap.c +++ b/src/eap-peap.c @@ -29,6 +29,7 @@ #include #include +#include "src/crypto.h" #include "src/missing.h" #include "src/eap.h" #include "src/eap-private.h" @@ -117,9 +118,170 @@ enum eap_extensions_tlv_type { /* Reserved = 0x0000, */ /* Reserved = 0x0001, */ /* Reserved = 0x0002, */ - EAP_EXTENSIONS_TLV_TYPE_RESULT = 0x8003, + EAP_EXTENSIONS_TLV_TYPE_RESULT = 0x8003, + EAP_EXTENSIONS_TLV_TYPE_CRYPTOBINDING = 0x000C, }; +enum TLV_CRYPTOBINDING_TYPE { + TLV_CRYPTOBINDING_TYPE_REQUEST = 0, + TLV_CRYPTOBINDING_TYPE_RESPONSE = 1, +}; + +static bool cryptobinding_tlv_generate_csk(struct eap_state *eap, uint8_t *imck) +{ + struct peap_state *peap_state = eap_tls_common_get_variant_data(eap); + static const char *label = "Session Key Generating Function"; + + if (!prf_plus_sha1(imck, 40, label, strlen(label), "\00", 1, + peap_state->key, sizeof(peap_state->key))) + return false; + + return true; +} + +static bool cryptobinding_tlv_generate_imck(struct eap_state *eap, + uint8_t *imck_out) +{ + struct peap_state *peap_state = eap_tls_common_get_variant_data(eap); + static const char *label = "Inner Methods Compound Keys"; + uint8_t isk[32]; + + memset(isk, 0, sizeof(isk)); + + if (!prf_plus_sha1(peap_state->key, 40, label, strlen(label), + isk, sizeof(isk), imck_out, 60)) + return false; + + return true; +} + +static int eap_extensions_handle_cryptobinding_tlv(struct eap_state *eap, + const uint8_t *data, + uint16_t tlv_value_len, + uint8_t *response) +{ + static const uint8_t cryptobinding_val_len = 56; + static const uint8_t cryptobinding_compound_mac_len = 20; + static const uint8_t cryptobinding_nonce_len = 32; + const uint8_t *nonce; + const uint8_t *server_compound_mac; + uint8_t client_compound_mac[cryptobinding_compound_mac_len]; + const uint8_t *cryptobinding_tlv_value; + uint8_t buf[61]; + uint8_t imck[60]; + + if (tlv_value_len != cryptobinding_val_len) + return -EBADMSG; + + cryptobinding_tlv_value = data; + + /* Reserved byte: must be ignored on receipt. */ + data += 1; + + /* Version byte: must be set to 0. */ + if (*data) + return -EBADMSG; + + data += 1; + + /* RecvVersion byte: must be set to 0. */ + if (*data) + return -EBADMSG; + + data += 1; + + /* SubType byte: cryptobinding TLV request. */ + if (*data != TLV_CRYPTOBINDING_TYPE_REQUEST) + return -EBADMSG; + + data += 1; + + nonce = data; + data += cryptobinding_nonce_len; + + server_compound_mac = data; + + l_put_be16(EAP_EXTENSIONS_TLV_TYPE_CRYPTOBINDING, &buf[0]); + l_put_be16(tlv_value_len, &buf[2]); + memcpy(&buf[4], cryptobinding_tlv_value, + 4 + cryptobinding_nonce_len); + memset(&buf[EAP_EXTENSIONS_TLV_HEADER_LEN + 4 + + cryptobinding_nonce_len], + 0, cryptobinding_compound_mac_len); + buf[60] = EAP_TYPE_PEAP; + + if (!cryptobinding_tlv_generate_imck(eap, imck)) { + l_error("PEAP: Failed to generate IMCK to validate " + "server compound MAC."); + + return -EIO; + } + + if (!hmac_sha1(imck + 40, 20, buf, sizeof(buf), client_compound_mac, + cryptobinding_compound_mac_len)) { + l_error("PEAP: Failed to generate compound MAC to validate " + "server compound MAC."); + + return -EIO; + } + + if (memcmp(server_compound_mac, client_compound_mac, + cryptobinding_compound_mac_len)) { + l_error("PEAP: Generated compound MAC and server compound MAC " + "don't match."); + + return -EIO; + } + + /* Build response Crypto-Binding TLV */ + data = response; + + l_put_be16(EAP_EXTENSIONS_TLV_TYPE_CRYPTOBINDING, response); + response += 2; + + l_put_be16(cryptobinding_val_len, response); + response += 2; + + /* Reserved - must be set to 0. */ + l_put_u8(0, response); + response += 1; + + /* Version */ + l_put_u8(EAP_TLS_VERSION_0, response); + response += 1; + + /* Received Version */ + l_put_u8(EAP_TLS_VERSION_0, response); + response += 1; + + /* Sub-Type */ + l_put_u8(TLV_CRYPTOBINDING_TYPE_RESPONSE, response); + response += 1; + + memcpy(response, nonce, cryptobinding_nonce_len); + response += cryptobinding_nonce_len; + + memcpy(buf, data, EAP_EXTENSIONS_TLV_HEADER_LEN + 4 + + cryptobinding_nonce_len); + + if (!hmac_sha1(imck + 40, 20, buf, sizeof(buf), client_compound_mac, + cryptobinding_compound_mac_len)) { + l_error("PEAP: Failed to generate client compound MAC."); + + return -EIO; + } + + memcpy(response, client_compound_mac, cryptobinding_compound_mac_len); + + if (!cryptobinding_tlv_generate_csk(eap, imck)) { + l_error("PEAP: Failed to generate Compound Session Key."); + + return -EIO; + } + + return EAP_EXTENSIONS_TLV_HEADER_LEN + cryptobinding_val_len; +} + enum eap_extensions_result { EAP_EXTENSIONS_RESULT_SUCCCESS = 1, EAP_EXTENSIONS_RESULT_FAILURE = 2, @@ -198,6 +360,12 @@ static int eap_extensions_process_tlvs(struct eap_state *eap, data, tlv_value_len, response, result); + break; + case EAP_EXTENSIONS_TLV_TYPE_CRYPTOBINDING: + response_tlv_len = + eap_extensions_handle_cryptobinding_tlv(eap, + data, tlv_value_len, response); + break; default: if (tlv_type & EAP_EXTENSIONS_TLV_M_BIT_MASK)