[Assignment-7] add rsa blinding against time based side channel attacks

Assignment 7 - SGX Hands-on/rsa/rsa.c

@@ -20,6 +20,7 @@ static int random_prime(mpz_t prime, const size_t size) {
 }
 
 static int rsa_keygen(rsa_key *key) {
+    // null pointer handling
     if(key == NULL)
         return 0;
 
@@ -31,9 +32,6 @@ static int rsa_keygen(rsa_key *key) {
     if ((!random_prime(key->p, MODULUS_SIZE/2)) || (!random_prime(key->q, MODULUS_SIZE/2)))
         return 0;
 
-    //printf("%d\n", mpz_probab_prime_p(key->p, 50));
-    //printf("%d\n", mpz_probab_prime_p(key->q, 50));
-
     // compute n
     mpz_mul(key->n, key->p, key->q);
 
@@ -55,12 +53,30 @@ static int rsa_keygen(rsa_key *key) {
     return 1;
 }
 
+static int rsa_export(rsa_key *key) {
+    
+}
+
+static int rsa_import(rsa_key *key) {
+    return 0;
+}
+
 int rsa_init(rsa_key *key) {
-    if(1) {
+    if(rsa_import(key)) {
-        return rsa_keygen(key);
+        return 1;
     } else {
-        // TODO: get from sealing
+        return rsa_keygen(key);
     }
+    return 0;
+}
+
+int rsa_public_init(rsa_public_key *key) {
+    // null pointer handling
+    if(key == NULL)
+        return 0;
+
+    mpz_init_set_ui(key->e, 65537);
+    mpz_init_set_str(key->n, "", 0);
 }
 
 void rsa_free(rsa_key *key) {
@@ -68,6 +84,11 @@ void rsa_free(rsa_key *key) {
     mpz_clears(key->p, key->q, key->n, key->e, key->d, NULL);
 }
 
+void rsa_public_free(rsa_public_key *key) {
+    // free bignums
+    mpz_clears(key->e, key->n, NULL);
+}
+
 static int pkcs1(mpz_t message, const u8 *data, const size_t length) {
     // temporary buffer
     u8 padded_bytes[MODULUS_SIZE];
@@ -98,40 +119,53 @@ static int pkcs1(mpz_t message, const u8 *data, const size_t length) {
     return 1;
 }
 
-// TODO RSA Blinding
+size_t rsa_sign(u8 *sig, const u8 *sha256, const rsa_key *key) {
-int rsa_sign(u8 *sig, const u8 *sha256, const rsa_key *key) {
     // null pointer handling
     if((sig == NULL) || (sha256 == NULL) || (key == NULL))
         return 0;
     
     // init bignum message
     mpz_t message; mpz_init(message);
+    mpz_t blinder; mpz_init(blinder);
+
+    // get random blinder
+    random_prime(blinder, MODULUS_SIZE - 10);
 
     // add padding
     if(!pkcs1(message, sha256, 32)) {
         return 0;
     }
 
+    // blind
+    mpz_mul(message, message, blinder);
+    mpz_mod(message, message, key->n);
+    mpz_invert(blinder, blinder, key->n);
+    mpz_powm(blinder, blinder, key->d, key->n);
+
     // compute signature
     mpz_powm(message, message, key->d, key->n);
 
+    // unblind
+    mpz_mul(message, message, blinder);
+    mpz_mod(message, message, key->n);
+
     // export signature
     size_t size = (mpz_sizeinbase(message, 2) + 7) / 8;
     mpz_export(sig, &size, 1, 1, 0, 0, message);
 
     // free bignum and return true
-    mpz_clear(message);
+    mpz_clears(message, blinder, NULL);
-    return 1;
+    return size;
 }
 
-
+int rsa_verify(const u8 *sig, const size_t sig_length, const u8 *sha256, const rsa_public_key *pk) {
-int rsa_verify(const u8 *sig, const size_t sig_length, u8 *sha256, rsa_public_key *pk) {
     // null pointer handling
     if((sig == NULL) || (sha256 == NULL) || (pk == NULL))
         return 0;
 
     // initialize bignums
-    mpz_t signature, message; mpz_inits(signature, message, NULL);
+    mpz_t signature, message; 
+    mpz_inits(signature, message, NULL);
 
     // import signature
     mpz_import(signature, (sig_length < MODULUS_SIZE) ? sig_length : MODULUS_SIZE, 1, 1, 0, 0, sig);
@@ -142,7 +176,7 @@ int rsa_verify(const u8 *sig, const size_t sig_length, u8 *sha256, rsa_public_ke
     // rebuild signed message
     if(!pkcs1(message, sha256, 32))
         return 0;
-
+    
     // compare signature with expected value
     if(mpz_cmp(signature, message) != 0)
         return 0;
@@ -152,10 +186,15 @@ int rsa_verify(const u8 *sig, const size_t sig_length, u8 *sha256, rsa_public_ke
     return 1;
 }
 
-void rsa_print(rsa_key *key) {
+void rsa_print(const rsa_key *key) {
-    gmp_printf("%Zu\n", key->p);
+    gmp_printf("%Zx\n", key->p);
-    gmp_printf("%Zu\n", key->q);
+    gmp_printf("%Zx\n", key->q);
-    gmp_printf("%Zu\n", key->n);
+    gmp_printf("%Zx\n", key->n);
-    gmp_printf("%Zu\n", key->e);
+    gmp_printf("%Zx\n", key->e);
-    gmp_printf("%Zu\n", key->d);
+    gmp_printf("%Zx\n", key->d);
+}
+
+void rsa_public_print(const rsa_public_key *pk) {
+    gmp_printf("%Zx\n", pk->e);
+    gmp_printf("%Zx\n", pk->n);
 }

Assignment 7 - SGX Hands-on/rsa/rsa.h

@@ -26,12 +26,16 @@ typedef struct {
     mpz_t n;
 } rsa_public_key;
 
-void rsa_print(rsa_key *key);
+void rsa_print(const rsa_key *key);
+void rsa_public_print(const rsa_public_key *pk);
 
 int rsa_init(rsa_key *key);
 void rsa_free(rsa_key *key);
 
-int rsa_sign(u8 *sig, const u8 *sha256, const rsa_key *key);
+int rsa_public_init(rsa_public_key *key);
-int rsa_verify(const u8 *sig, const size_t sig_length, u8 *sha256, rsa_public_key *pk);
+void rsa_public_free(rsa_public_key *key);
+
+size_t rsa_sign(u8 *sig, const u8 *sha256, const rsa_key *key);
+int rsa_verify(const u8 *sig, const size_t sig_length, const u8 *sha256, const rsa_public_key *pk);
 
 #endif