Refactor key loading code.

1 files changed, 95 insertions, 57 deletions

diff --git a/rsa.c b/rsa.c
index 31c4f61..0d3ae69 100644
--- a/rsa.c
+++ b/rsa.c
@@ -96,10 +96,8 @@ void hal_rsa_set_debug(const int onoff)
  * can make memory allocation the caller's problem (well, maybe).
  */
 
-typedef enum { RSA_PRIVATE, RSA_PUBLIC } rsa_key_type_t;
-
-typedef struct {
-  rsa_key_type_t type;          /* What kind of key this is */
+struct rsa_key {
+  hal_rsa_key_type_t type;      /* What kind of key this is */
   fp_int n;                     /* The modulus */
   fp_int e;                     /* Public exponent */
   fp_int d;                     /* Private exponent */
@@ -108,9 +106,9 @@ typedef struct {
   fp_int u;                     /* 1/q mod p */
   fp_int dP;                    /* d mod (p - 1) */
   fp_int dQ;                    /* d mod (q - 1) */
-} rsa_key_t;
+};
 
-const size_t hal_rsa_key_t_size = sizeof(rsa_key_t);
+const size_t hal_rsa_key_t_size = sizeof(struct rsa_key);
 
 /*
  * In the long run we want a full RSA implementation, or enough of one
@@ -134,7 +132,7 @@ const size_t hal_rsa_key_t_size = sizeof(rsa_key_t);
     case FP_OKAY: break;                                \
     case FP_VAL:  lose(HAL_ERROR_BAD_ARGUMENTS);        \
     case FP_MEM:  lose(HAL_ERROR_ALLOCATION_FAILURE);   \
-    default:      lose(HAL_ERROR_UNKNOWN_TFM_FAILURE);  \
+    default:      lose(HAL_ERROR_IMPOSSIBLE);  		\
     }                                                   \
   } while (0)
 
@@ -162,13 +160,10 @@ static hal_error_t unpack_fp(fp_int *bn, uint8_t *buffer, const size_t length)
 }
 
 /*
- * modexp_fp() is a function I haven't written yet which takes
- * fp_int values, unwraps them, feeds the numbers into hal_modexp(),
- * and wraps the result back up as a fp_int.
+ * Unwrap bignums into byte arrays, feeds them into hal_modexp(), and
+ * wrap result back up as a bignum.
  */
 
-/* modexp_fp(&tmp.msg, &key.dP, &key.p, &tmp.m1) */
-
 static hal_error_t modexp_fp(fp_int *msg, fp_int *exp, fp_int *mod, fp_int *res)
 {
   hal_error_t err = HAL_OK;
@@ -201,81 +196,124 @@ static hal_error_t modexp_fp(fp_int *msg, fp_int *exp, fp_int *mod, fp_int *res)
   return err;
 }
 
+
 /*
- * CRT with the components we have.  PyCrypto doesn't give us dP or
- * dQ, probably because they're so easy to calculate that it's
- * (almost) not worth the bother.
+ * Clear a key.  We might want to do something a bit more energetic
+ * than plain old memset() eventually.
  */
 
-hal_error_t hal_rsa_crt(const uint8_t * const m, const size_t m_len,
-                        const uint8_t * const n, const size_t n_len,
-                        const uint8_t * const e, const size_t e_len,
-                        const uint8_t * const d, const size_t d_len,
-                        const uint8_t * const p, const size_t p_len,
-                        const uint8_t * const q, const size_t q_len,
-                        const uint8_t * const u, const size_t u_len,
-                        uint8_t * result, const size_t result_len)
+void hal_rsa_key_clear(hal_rsa_key_t key)
 {
-  hal_error_t err = HAL_OK;
-  rsa_key_t key;
-  struct { fp_int t, msg, m1, m2; } tmp;
+  if (key.key != NULL)
+    memset(key.key, 0, sizeof(struct rsa_key));
+}
 
-  key.type = RSA_PRIVATE;
+/*
+ * Load a key from raw components.  This is a simplistic version: we
+ * don't attempt to generate missing private key components, we just
+ * reject the key if it doesn't have everything we expect.
+ *
+ * In theory, the only things we'd really need for the private key if
+ * we were being nicer about this would be e, p, and q, as we could
+ * calculate everything else from them.
+ */
+
+hal_error_t hal_rsa_key_load(const hal_rsa_key_type_t type,
+                             hal_rsa_key_t *key_,
+                             void *keybuf, const size_t keybuf_len,
+                             const uint8_t * const n,  const size_t n_len,
+                             const uint8_t * const e,  const size_t e_len,
+                             const uint8_t * const d,  const size_t d_len,
+                             const uint8_t * const p,  const size_t p_len,
+                             const uint8_t * const q,  const size_t q_len,
+                             const uint8_t * const u,  const size_t u_len,
+                             const uint8_t * const dP, const size_t dP_len,
+                             const uint8_t * const dQ, const size_t dQ_len)
+{
+  if (key_ == NULL || keybuf == NULL || keybuf_len < sizeof(struct rsa_key))
+    return HAL_ERROR_BAD_ARGUMENTS;
+
+  memset(keybuf, 0, keybuf_len);
 
-#define _(x) do { fp_init(&key.x); fp_read_unsigned_bin(&key.x, (uint8_t *) x, x##_len); } while (0)
-  _(n); _(e); _(d); _(p); _(q); _(u);
+  struct rsa_key *key = keybuf;
+
+  key->type = type;
+
+#define _(x) do { fp_init(&key->x); if (x == NULL) goto fail; fp_read_unsigned_bin(&key->x, (uint8_t *) x, x##_len); } while (0)
+  switch (type) {
+  case RSA_PRIVATE:
+    _(d); _(p); _(q); _(u); _(dP); _(dQ);
+  case RSA_PUBLIC:
+    _(n); _(e);
+    key_->key = key;
+    return HAL_OK;
+  }
 #undef _
 
+ fail:
+  memset(key, 0, sizeof(*key));
+  return HAL_ERROR_BAD_ARGUMENTS;
+}
+
+/*
+ * RSA decyrption/signature using the Chinese Remainder Theorem
+ * (Garner's formula).
+ */
+
+hal_error_t hal_rsa_crt(hal_rsa_key_t key_,
+                        const uint8_t * const m,  const size_t m_len,
+                        uint8_t * result, const size_t result_len)
+{
+  hal_error_t err = HAL_OK;
+  struct rsa_key *key = key_.key;
+  struct { fp_int t, msg, m1, m2; } tmp;
+
   fp_init(&tmp.t);
   fp_init(&tmp.msg);
   fp_init(&tmp.m1);
   fp_init(&tmp.m2);
 
-  /* Calculate dP = d % (p-1) and dQ = d % (q-1) */
-
-  fp_sub_d(&key.p, 1, &tmp.t);
-  FP_CHECK(fp_mod(&key.d, &tmp.t, &key.dP));
-
-  fp_sub_d(&key.q, 1, &tmp.t);
-  FP_CHECK(fp_mod(&key.d, &tmp.t, &key.dQ));
-
-  /* Read message to be signed/decrypted into a bignum */
-
   fp_read_unsigned_bin(&tmp.msg, (uint8_t *) m, m_len);
 
-  /* OK, try to perform the CRT */
-
-  /* m1 = msg ** dP mod p, m2 = msg ** dQ mod q */
-  if ((err = modexp_fp(&tmp.msg, &key.dP, &key.p, &tmp.m1)) != HAL_OK ||
-      (err = modexp_fp(&tmp.msg, &key.dQ, &key.q, &tmp.m2)) != HAL_OK)
+  /*
+   * m1 = msg ** dP mod p
+   * m2 = msg ** dQ mod q
+   */
+  if ((err = modexp_fp(&tmp.msg, &key->dP, &key->p, &tmp.m1)) != HAL_OK ||
+      (err = modexp_fp(&tmp.msg, &key->dQ, &key->q, &tmp.m2)) != HAL_OK)
     goto fail;
 
-  /* t = m1 - m2 */
+  /*
+   * t = m1 - m2.
+   * Add zero (mod p) once or twice if necessary to get positive result.
+   */
   fp_sub(&tmp.m1, &tmp.m2, &tmp.t);
-
-  /* Add zero (mod p) if necessary to get positive result */
   if (fp_cmp_d(&tmp.t, 0) == FP_LT)
-    fp_add(&tmp.t, &key.p, &tmp.t);
+    fp_add(&tmp.t, &key->p, &tmp.t);
   if (fp_cmp_d(&tmp.t, 0) == FP_LT)
-    fp_add(&tmp.t, &key.p, &tmp.t);
+    fp_add(&tmp.t, &key->p, &tmp.t);
   if (fp_cmp_d(&tmp.t, 0) == FP_LT)
-    lose(HAL_ERROR_CRT_FAILED);
+    lose(HAL_ERROR_IMPOSSIBLE);
 
-  /* t = (t * u mod p) * q + m2 */
-  FP_CHECK(fp_mulmod(&tmp.t, &key.u, &key.p, &tmp.t));
-  fp_mul(&tmp.t, &key.q, &tmp.t);
+  /*
+   * t = (t * u mod p) * q + m2
+   */
+  FP_CHECK(fp_mulmod(&tmp.t, &key->u, &key->p, &tmp.t));
+  fp_mul(&tmp.t, &key->q, &tmp.t);
   fp_add(&tmp.t, &tmp.m2, &tmp.t);
 
-  /* Have result, write it back to caller */
+  /*
+   * t now holds result, write it back to caller
+   */
   if ((err = unpack_fp(&tmp.t, result, result_len)) != HAL_OK)
     goto fail;
 
-  /* Done, fall through into cleanup code */
+  /*
+   * Done, fall through into cleanup.
+   */
 
  fail:
-  memset(&key, 0, sizeof(key));
   memset(&tmp, 0, sizeof(tmp));
-
   return err;
 }