From 8020e868f92153a49c1f9b4fbead13b89ee64267 Mon Sep 17 00:00:00 2001
From: Conor Patrick <conorpp@vt.edu>
Date: Fri, 18 May 2018 12:20:22 -0400
Subject: [PATCH] verify the pinAuth parameter with hmac

---
 crypto.c | 38 ++++++++++++++++++++++++++++++++++++++
 crypto.h |  1 +
 ctap.c   | 34 +++++++++++++++++++++++++++++++++-
 3 files changed, 72 insertions(+), 1 deletion(-)

diff --git a/crypto.c b/crypto.c
index 1e7bddb..cb2614a 100644
--- a/crypto.c
+++ b/crypto.c
@@ -54,6 +54,44 @@ void crypto_sha256_final(uint8_t * hash)
     sha256_final(&sha256_ctx, hash);
 }
 
+void crypto_sha256_hmac(uint8_t * key, uint32_t klen, uint8_t * data, uint32_t datalen, uint8_t * hmac)
+{
+    uint8_t buf[64];
+    int i;
+    memset(buf, 0, sizeof(buf));
+
+    if(klen > 64)
+    {
+        printf("Error, key size must be <= 64\n");
+        exit(1);
+    }
+
+    memmove(buf, key, klen);
+
+    for (i = 0; i < sizeof(buf); i++)
+    {
+        buf[i] = buf[i] ^ 0x36;
+    }
+
+    crypto_sha256_init();
+    crypto_sha256_update(buf, 64);
+    crypto_sha256_update(data, datalen);
+    crypto_sha256_final(hmac);
+
+    memset(buf, 0, sizeof(buf));
+    memmove(buf, key, klen);
+
+    for (i = 0; i < sizeof(buf); i++)
+    {
+        buf[i] = buf[i] ^ 0x5c;
+    }
+
+    crypto_sha256_init();
+    crypto_sha256_update(buf, 64);
+    crypto_sha256_update(hmac, 32);
+    crypto_sha256_final(hmac);
+}
+
 
 void crypto_ecc256_init()
 {
diff --git a/crypto.h b/crypto.h
index 2742f8f..af64dcb 100644
--- a/crypto.h
+++ b/crypto.h
@@ -9,6 +9,7 @@ void crypto_sha256_update(uint8_t * data, size_t len);
 void crypto_sha256_update_secret();
 void crypto_sha256_final(uint8_t * hash);
 
+void crypto_sha256_hmac(uint8_t * key, uint32_t klen, uint8_t * data, uint32_t datalen, uint8_t * hmac);
 
 void crypto_ecc256_init();
 void crypto_ecc256_derive_public_key(uint8_t * data, int len, uint8_t * x, uint8_t * y);
diff --git a/ctap.c b/ctap.c
index 9f8c17a..f1758f3 100644
--- a/ctap.c
+++ b/ctap.c
@@ -117,6 +117,26 @@ static const char * cbor_value_get_type_string(const CborValue *value)
     /*return CborNoError;*/
 /*}*/
 
+uint8_t verify_pin_auth(uint8_t * pinAuth, uint8_t * clientDataHash)
+{
+    uint8_t hmac[32];
+    crypto_sha256_hmac(PIN_TOKEN, PIN_TOKEN_SIZE, clientDataHash, CLIENT_DATA_HASH_SIZE, hmac);
+
+    if (memcmp(pinAuth, hmac, 16) == 0)
+    {
+        return 0;
+    }
+    else
+    {
+        printf2(TAG_ERR,"Pin auth failed\n");
+        dump_hex1(TAG_ERR,pinAuth,16);
+        dump_hex1(TAG_ERR,hmac,16);
+        return CTAP2_ERR_PIN_AUTH_INVALID;
+    }
+
+}
+
+
 uint8_t ctap_get_info(CborEncoder * encoder)
 {
     int ret;
@@ -1036,6 +1056,12 @@ uint8_t ctap_make_credential(CborEncoder * encoder, uint8_t * request, int lengt
         printf2(TAG_ERR,"pinAuth is required\n");
         return CTAP2_ERR_PIN_REQUIRED;
     }
+    else
+    {
+        ret = verify_pin_auth(MC.pinAuth, MC.clientDataHash);
+        check_retr(ret);
+    }
+
 
 
     CborEncoder map;
@@ -1393,6 +1419,11 @@ uint8_t ctap_get_assertion(CborEncoder * encoder, uint8_t * request, int length)
         printf2(TAG_ERR,"pinAuth is required\n");
         return CTAP2_ERR_PIN_REQUIRED;
     }
+    else
+    {
+        ret = verify_pin_auth(GA.pinAuth, GA.clientDataHash);
+        check_retr(ret);
+    }
 
 
     CborEncoder map;
@@ -1700,6 +1731,7 @@ uint8_t ctap_add_pin_if_verified(CborEncoder * map, uint8_t * platform_pubkey, u
         printf2(TAG_ERR,"Pin does not match!\n");
         printf2(TAG_ERR,"platform-pin-hash: "); dump_hex1(TAG_ERR, pinHashEnc, 16);
         printf2(TAG_ERR,"authentic-pin-hash: "); dump_hex1(TAG_ERR, PIN_CODE_HASH, 16);
+        // Generate new keyAgreement pair
         crypto_ecc256_make_key_pair(KEY_AGREEMENT_PUB, KEY_AGREEMENT_PRIV);
         return CTAP2_ERR_PIN_INVALID;
     }
@@ -1882,7 +1914,7 @@ void ctap_init()
 
     crypto_ecc256_make_key_pair(KEY_AGREEMENT_PUB, KEY_AGREEMENT_PRIV);
 
-    // TODO this should be stored in flash memory
+    // TODO this doesn't have to happen at every boot up
     memset(PIN_CODE,0,sizeof(PIN_CODE));
     memmove(PIN_CODE, "1234", 4);
     PIN_CODE_SET = 1;