Add AES Key Wrap using Cryptech AES core.

1 files changed, 261 insertions, 0 deletions

diff --git a/aes_keywrap.c b/aes_keywrap.c
new file mode 100644
index 0000000..b8f505f
--- /dev/null
+++ b/aes_keywrap.c
@@ -0,0 +1,261 @@
+/*
+ * Implementation of RFC 5649 variant of AES Key Wrap, using Cryptlib
+ * to supply the AES ECB encryption and decryption functions.
+ *
+ * Note that there are two different block sizes involved here: the
+ * key wrap algorithm deals entirely with 64-bit blocks, while AES
+ * itself deals with 128-bit blocks.  In practice, this is not as
+ * confusing as it sounds, because we combine two 64-bit blocks to
+ * create one 128-bit block just prior to performing an AES operation,
+ * then split the result back to 64-bit blocks immediately afterwards.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+#include <assert.h>
+
+#include "cryptech.h"
+
+
+/*
+ * How long the ciphertext will be for a given plaintext length.
+ */
+
+size_t hal_aes_keywrap_ciphertext_length(const size_t plaintext_length)
+{
+  return (plaintext_length + 15) & ~7;
+}
+
+
+/*
+ * Check the KEK, then load it into the AES core.
+ * Note that our AES core only supports 128 and 256 bit keys.
+ */
+
+typedef enum { KEK_encrypting, KEK_decrypting } kek_action_t;
+
+static hal_error_t load_kek(const uint8_t *K, const size_t K_len, const kek_action_t action)
+{
+  uint8_t config[4];
+  hal_error_t err;
+
+  if (K == NULL)
+    return HAL_ERROR_BAD_ARGUMENTS;
+
+  memset(config, 0, sizeof(config));
+
+  switch (K_len) {
+  case bitsToBytes(128):
+    config[3] &= ~AES_CONFIG_KEYLEN;
+    break;
+  case bitsToBytes(256):
+    config[3] |=  AES_CONFIG_KEYLEN;
+    break;
+  default:
+    return HAL_ERROR_BAD_ARGUMENTS;
+  }
+
+  switch (action) {
+  case KEK_encrypting:
+    config[3] |=  AES_CONFIG_ENCDEC;
+    break;
+  case KEK_decrypting:
+    config[3] &= !AES_CONFIG_ENCDEC;
+    break;
+  default:
+    return HAL_ERROR_BAD_ARGUMENTS;
+  }
+
+  /*
+   * Load the KEK and tell the core to expand it.
+   */
+
+  if ((err = hal_io_write(AES_ADDR_KEY0, K, K_len)) != HAL_OK ||
+      (err = hal_io_init(AES_ADDR_CTRL))            != HAL_OK)
+    return err;
+
+  return HAL_OK;
+}
+
+
+/*
+ * Process one block.  Since AES Key Wrap always deals with 64-bit
+ * half blocks and since the bus is going to break this up into 32-bit
+ * words no matter what we do, we can eliminate a few gratuitous
+ * memcpy() operations by receiving our arguments as two half blocks.
+ *
+ * Since the length of these half blocks is constant, there's no real
+ * point in passing the length as an argument, we'd just be checking a
+ * constant against a constant and a smart compiler will optimize
+ * the whole check out.
+ *
+ * Just be VERY careful if you change anything here.
+ */
+
+static hal_error_t do_block(uint8_t *b1, uint8_t *b2)
+{
+  hal_error_t err;
+
+  assert(b1 != NULL && b2 != NULL);
+
+  if ((err = hal_io_write(AES_ADDR_BLOCK0, b1, 8)) != HAL_OK ||
+      (err = hal_io_write(AES_ADDR_BLOCK2, b2, 8)) != HAL_OK ||
+      (err = hal_io_next(AES_ADDR_CTRL))           != HAL_OK ||
+      (err = hal_io_wait_ready(AES_ADDR_STATUS))   != HAL_OK ||
+      (err = hal_io_read(AES_ADDR_RESULT0, b1, 8)) != HAL_OK ||
+      (err = hal_io_read(AES_ADDR_RESULT2, b2, 8)) != HAL_OK)
+    return err;
+
+  return HAL_OK;
+}
+
+
+/*
+ * Wrap plaintext Q using KEK K, placing result in C.
+ *
+ * Q and C can overlap.  For encrypt-in-place, use Q = C + 8 (that is,
+ * leave 8 empty bytes before the plaintext).
+ *
+ * Use hal_aes_keywrap_ciphertext_length() to calculate the correct
+ * buffer size.
+ */
+
+hal_error_t hal_aes_keywrap(const uint8_t *K, const size_t K_len,
+                            const uint8_t * const Q,
+                            const size_t m,
+                            uint8_t *C,
+                            size_t *C_len)
+{
+  const size_t calculated_C_len = hal_aes_keywrap_ciphertext_length(m);
+  hal_error_t err;
+  uint32_t n;
+  long i, j;
+
+  assert(calculated_C_len % 8 == 0);
+
+  if (Q == NULL || C == NULL || C_len == NULL || *C_len < calculated_C_len)
+    return HAL_ERROR_BAD_ARGUMENTS;
+
+  if ((err = load_kek(K, K_len, KEK_encrypting)) != HAL_OK)
+    return err;
+
+  *C_len = calculated_C_len;
+
+  if (C + 8 != Q)
+    memmove(C + 8, Q, m);
+  if (m % 8 != 0)
+    memset(C + 8 + m, 0, 8 -  (m % 8));
+  C[0] = 0xA6;
+  C[1] = 0x59;
+  C[2] = 0x59;
+  C[3] = 0xA6;
+  C[4] = (m >> 24) & 0xFF;
+  C[5] = (m >> 16) & 0xFF;
+  C[6] = (m >>  8) & 0xFF;
+  C[7] = (m >>  0) & 0xFF;
+
+  n = calculated_C_len/8 - 1;
+
+  if (n == 1) {
+    if ((err = do_block(C, C + 8)) != HAL_OK)
+      return err;
+  }
+
+  else {
+    for (j = 0; j <= 5; j++) {
+      for (i = 1; i <= n; i++) {
+        uint32_t t = n * j + i;
+        if ((err = do_block(C, C + i * 8)) != HAL_OK)
+          return err;
+        C[7] ^= t & 0xFF; t >>= 8;
+        C[6] ^= t & 0xFF; t >>= 8;
+        C[5] ^= t & 0xFF; t >>= 8;
+        C[4] ^= t & 0xFF;
+      }
+    }
+  }
+
+  return HAL_OK;
+}
+
+
+/*
+ * Unwrap ciphertext C using KEK K, placing result in Q.
+ *
+ * Q should be the same size as C.  Q and C can overlap.
+ */
+
+hal_error_t hal_aes_keyunwrap(const uint8_t *K, const size_t K_len,
+                              const uint8_t * const C,
+                              const size_t C_len,
+                              uint8_t *Q,
+                              size_t *Q_len)
+{
+  hal_error_t err;
+  uint32_t n;
+  long i, j;
+  size_t m;
+
+  if (C == NULL || Q == NULL || C_len % 8 != 0 || C_len < 16 || Q_len == NULL || *Q_len < C_len)
+    return HAL_ERROR_BAD_ARGUMENTS;
+
+  if ((err = load_kek(K, K_len, KEK_decrypting)) != HAL_OK)
+    return err;
+
+  n = (C_len / 8) - 1;
+
+  if (Q != C)
+    memmove(Q, C, C_len);
+
+  if (n == 1) {
+    if ((err = do_block(Q, Q + 8)) != HAL_OK)
+      return err;
+  }
+
+  else {
+    for (j = 5; j >= 0; j--) {
+      for (i = n; i >= 1; i--) {
+        uint32_t t = n * j + i;
+        Q[7] ^= t & 0xFF; t >>= 8;
+        Q[6] ^= t & 0xFF; t >>= 8;
+        Q[5] ^= t & 0xFF; t >>= 8;
+        Q[4] ^= t & 0xFF;
+        if ((err = do_block(Q, Q + i * 8)) != HAL_OK)
+          return err;
+      }
+    }
+  }
+
+  if (Q[0] != 0xA6 || Q[1] != 0x59 || Q[2] != 0x59 || Q[3] != 0xA6)
+    return HAL_ERROR_KEYWRAP_BAD_MAGIC;
+
+  m = (((((Q[4] << 8) + Q[5]) << 8) + Q[6]) << 8) + Q[7];
+
+  if (m <= 8 * (n - 1) || m > 8 * n)
+    return HAL_ERROR_KEYWRAP_BAD_LENGTH;
+
+  if (m % 8 != 0)
+    for (i = m + 8; i < 8 * (n + 1); i++)
+      if (Q[i] != 0x00)
+        return HAL_ERROR_KEYWRAP_BAD_PADDING;
+
+  *Q_len = m;
+
+  memmove(Q, Q + 8, m);
+
+  return HAL_OK;
+}
+
+/*
+ * "Any programmer who fails to comply with the standard naming, formatting,
+ *  or commenting conventions should be shot.  If it so happens that it is
+ *  inconvenient to shoot him, then he is to be politely requested to recode
+ *  his program in adherence to the above standard."
+ *                      -- Michael Spier, Digital Equipment Corporation
+ *
+ * Local variables:
+ * indent-tabs-mode: nil
+ * End:
+ */