Snapshot along the way to ECDSA. Code mostly written, except for

ecdsa_verify().  Untested.  Point addition and doubling algorithms are
the ones from libtomcrypt, main point of this commit is to save those
before replacing them with faster algorithms from hyperelliptic.org.

1 files changed, 206 insertions, 0 deletions

diff --git a/asn1.c b/asn1.c
new file mode 100644
index 0000000..f4b3610
--- /dev/null
+++ b/asn1.c
@@ -0,0 +1,206 @@
+/*
+ * asn1.c
+ * ------
+ * Minimal ASN.1 implementation in support of Cryptech libhal.
+ *
+ * The functions in this module are not intended to be part of the
+ * public API.  Rather, these are utility functions used by more than
+ * one module within the library, which would otherwise have to be
+ * duplicated.  The main reason for keeping these private is to avoid
+ * having the public API depend on any details of the underlying
+ * bignum implementation (currently libtfm, but that might change).
+ *
+ * As of this writing, the ASN.1 support we need is quite minimal, so,
+ * rather than attempting to clean all the unecessary cruft out of a
+ * general purpose ASN.1 implementation, we hand code the very small
+ * number of data types we need.  At some point this will probably
+ * become impractical, at which point we might want to look into using
+ * something like the asn1c compiler.
+ *
+ * Authors: Rob Austein
+ * Copyright (c) 2015, SUNET
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <stddef.h>
+#include <string.h>
+#include <assert.h>
+
+#include "hal.h"
+
+#include "asn1_internal.h"
+
+/*
+ * Encode tag and length fields of an ASN.1 object.  If der is NULL,
+ * just return the size that would be encoded.
+ */
+
+hal_error_t hal_asn1_encode_header(const uint8_t tag,
+				   const size_t value_len,
+				   uint8_t *der, size_t *der_len, const size_t der_max)
+{
+  size_t header_len = 2;	/* Shortest encoding is one octet each for tag and length */
+
+  if (value_len >= 128)		/* Add octets for longer length encoding as needed */
+    for (size_t n = value_len; n > 0; n >>= 8)
+      ++header_len;
+
+  if (der_len != NULL)
+    *der_len = header_len;
+
+  if (der == NULL)		/* If caller just wanted the length, we're done */
+    return HAL_OK;
+
+  /*
+   * Make sure there's enough room for header + value, then encode.
+   */
+
+  if (value_len + header_len > der_max)
+    return HAL_ERROR_RESULT_TOO_LONG;
+
+  if (value_len < 128) {
+    *der = (uint8_t) value_len;
+  }
+
+  else {
+    *der = 0x80 | (uint8_t) (header_len -= 2);
+    for (size_t n = value_len; n > 0 && header_len > 0; n >>= 8)
+      der[header_len--] = (uint8_t) (n & 0xFF);
+  }
+
+  return HAL_OK;
+}
+
+/*
+ * Encode an unsigned ASN.1 INTEGER from a libtfm bignum.  If der is
+ * NULL, just return the length of what we would have encoded.
+ */
+
+hal_error_t hal_asn1_encode_integer(fp_int *bn,
+				    uint8_t *der, size_t *der_len, const size_t der_max)
+{
+  if (bn == NULL)
+    return HAL_ERROR_BAD_ARGUMENTS;
+
+  /*
+   * We only handle unsigned INTEGERs, so we need to pad data with a
+   * leading zero if the most significant bit is set, to avoid
+   * flipping the ASN.1 sign bit.  Conveniently, this also handles the
+   * difference between libtfm's and ASN.1's encoding of zero.
+   */
+
+  if (fp_cmp_d(bn, 0) == FP_LT)
+    return HAL_ERROR_BAD_ARGUMENTS;
+
+  const int leading_zero = fp_iszero(bn) || (fp_count_bits(bn) & 7) == 0;
+  const size_t vlen = fp_unsigned_bin_size(bn) + leading_zero;
+  hal_error_t err;
+  size_t hlen;
+
+  if ((err = hal_asn1_encode_header(ASN1_INTEGER, vlen, der, &hlen, der_max)) != HAL_OK)
+    return err;
+
+  if (der_len != NULL)
+    *der_len = hlen + vlen;
+
+  if (der == NULL)
+    return HAL_OK;
+
+  if (hlen + vlen > der_max)
+    return HAL_ERROR_RESULT_TOO_LONG;
+
+  der += hlen;
+  if (leading_zero)
+    *der++ = 0x00;
+  fp_to_unsigned_bin(bn, der);
+
+  return HAL_OK;
+}
+
+
+hal_error_t hal_asn1_decode_header(const uint8_t tag,
+				   const uint8_t * const der, size_t der_max,
+				   size_t *hlen, size_t *vlen)
+{
+  assert(der != NULL && hlen != NULL && vlen != NULL);
+
+  if (der_max < 2 || der[0] != tag)
+    return HAL_ERROR_ASN1_PARSE_FAILED;
+
+  if ((der[1] & 0x80) == 0) {
+    *hlen = 2;
+    *vlen = der[1];
+  }
+
+  else {
+    *hlen = 2 + (der[1] & 0x7F);
+    *vlen = 0;
+
+    if (*hlen > der_max)
+      return HAL_ERROR_ASN1_PARSE_FAILED;
+
+    for (size_t i = 2; i < *hlen; i++)
+      *vlen = (*vlen << 8) + der[i];
+  }
+
+  if (*hlen + *vlen > der_max)
+    return HAL_ERROR_ASN1_PARSE_FAILED;
+
+  return HAL_OK;
+}
+
+hal_error_t hal_asn1_decode_integer(fp_int *bn,
+				    const uint8_t * const der, size_t *der_len, const size_t der_max)
+{
+  if (bn == NULL || der == NULL)
+    return HAL_ERROR_BAD_ARGUMENTS;
+
+  hal_error_t err;
+  size_t hlen, vlen;
+
+  if ((err = hal_asn1_decode_header(ASN1_INTEGER, der, der_max, &hlen, &vlen)) != HAL_OK)
+    return err;
+
+  if (der_len != NULL)
+    *der_len = hlen + vlen;
+
+  if (vlen < 1 || (der[hlen] & 0x80) != 0x00)
+    return HAL_ERROR_ASN1_PARSE_FAILED;
+
+  fp_init(bn);
+  fp_read_unsigned_bin(bn, (uint8_t *) der + hlen, vlen);
+  return HAL_OK;
+}
+
+/*
+ * Local variables:
+ * indent-tabs-mode: nil
+ * End:
+ */