From a615b134c498f8d88e0dab047f40c7096a2f9e03 Mon Sep 17 00:00:00 2001
From: Rob Austein <sra@hactrn.net>
Date: Thu, 18 Jun 2015 18:44:40 -0400
Subject: Supply public exponent as bigendian byte string rather than unsigned
 long, since that's the form we'll need for PKCS #11.

---
 cryptech.h       |  3 +--
 rsa.c            | 32 +++++++++-----------------------
 tests/test-rsa.c |  4 +++-
 3 files changed, 13 insertions(+), 26 deletions(-)

diff --git a/cryptech.h b/cryptech.h
index 81f23f5..d8f1208 100644
--- a/cryptech.h
+++ b/cryptech.h
@@ -641,8 +641,7 @@ extern hal_error_t hal_rsa_decrypt(hal_rsa_key_t key,
 extern hal_error_t hal_rsa_key_gen(hal_rsa_key_t *key,
                                    void *keybuf, const size_t keybuf_len,
                                    const unsigned key_length,
-                                   const unsigned long public_exponent);
-
+                                   const uint8_t * const public_exponent, const size_t public_exponent_len);
 
 extern hal_error_t hal_rsa_key_to_der(hal_rsa_key_t key,
                                       uint8_t *der, size_t *der_len, const size_t der_max);
diff --git a/rsa.c b/rsa.c
index 9fe2c47..28365ae 100644
--- a/rsa.c
+++ b/rsa.c
@@ -201,7 +201,7 @@ static hal_error_t create_blinding_factors(struct rsa_key *key, fp_int *bf, fp_i
 {
   assert(key != NULL && bf != NULL && ubf != NULL);
 
-  uint8_t rnd[(fp_unsigned_bin_size(&key->n) + 7) & ~7];
+  uint8_t rnd[fp_unsigned_bin_size(&key->n)];
   hal_error_t err = HAL_OK;
 
   if ((err = hal_get_random(rnd, sizeof(rnd))) != HAL_OK)
@@ -443,7 +443,7 @@ static hal_error_t find_prime(unsigned prime_length, fp_int *e, fp_int *result)
 hal_error_t hal_rsa_key_gen(hal_rsa_key_t *key_,
                             void *keybuf, const size_t keybuf_len,
                             const unsigned key_length,
-                            const unsigned long public_exponent)
+                            const uint8_t * const public_exponent, const size_t public_exponent_len)
 {
   struct rsa_key *key = keybuf;
   hal_error_t err = HAL_OK;
@@ -452,30 +452,16 @@ hal_error_t hal_rsa_key_gen(hal_rsa_key_t *key_,
   if (key_ == NULL || keybuf == NULL || keybuf_len < sizeof(struct rsa_key))
     return HAL_ERROR_BAD_ARGUMENTS;
 
-  switch (key_length) {
-  case bitsToBytes(1024):
-  case bitsToBytes(2048):
-  case bitsToBytes(4096):
-  case bitsToBytes(8192):
-    break;
-  default:
-    return HAL_ERROR_UNSUPPORTED_KEY;
-  }
+  memset(keybuf, 0, keybuf_len);
+  key->type = HAL_RSA_PRIVATE;
+  fp_read_unsigned_bin(&key->e, (uint8_t *) public_exponent, public_exponent_len);
 
-  switch (public_exponent) {
-  case 0x010001:
-    break;
-  default:
+  if (key_length != bitsToBytes(1024) && key_length != bitsToBytes(2048) &&
+      key_length != bitsToBytes(4096) && key_length != bitsToBytes(8192))
     return HAL_ERROR_UNSUPPORTED_KEY;
-  }
 
-  /*
-   * Initialize key
-   */
-
-  memset(keybuf, 0, keybuf_len);
-  key->type = HAL_RSA_PRIVATE;
-  fp_set(&key->e, public_exponent);
+  if (fp_cmp_d(&key->e, 0x010001) != FP_EQ)
+    return HAL_ERROR_UNSUPPORTED_KEY;
 
   /*
    * Find a good pair of prime numbers.
diff --git a/tests/test-rsa.c b/tests/test-rsa.c
index 9b346b5..03ea8bb 100644
--- a/tests/test-rsa.c
+++ b/tests/test-rsa.c
@@ -133,7 +133,9 @@ static int test_gen(const char * const kind, const rsa_tc_t * const tc)
   hal_error_t err = HAL_OK;
   FILE *f;
 
-  if ((err = hal_rsa_key_gen(&key1, keybuf1, sizeof(keybuf1), bitsToBytes(tc->size), 0x010001)) != HAL_OK) {
+  const uint8_t f4[] = { 0x01, 0x00, 0x01 };
+
+  if ((err = hal_rsa_key_gen(&key1, keybuf1, sizeof(keybuf1), bitsToBytes(tc->size), f4, sizeof(f4))) != HAL_OK) {
     printf("RSA key generation failed: %s\n", hal_error_string(err));
     return 0;
   }
-- 
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