[Cryptech-Commits] [sw/libhal] 01/02: Tweak CRC input to be backwards compatabile with ksng.

[git at cryptech.is]

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sra at hactrn.net pushed a commit to branch ks9
in repository sw/libhal.

commit a83d9dfba5f882ca75eaab9a166e6ad9794f2f90
Author: Rob Austein <sra at hactrn.net>
AuthorDate: Sun Jun 4 12:21:45 2017 -0400

    Tweak CRC input to be backwards compatabile with ksng.
    
    Except for torture tests, we never really used the hideously complex
    multi-block capabilities of the ksng version of the flash keystore,
    among other reasons because the only keys large enough to trigger the
    multi-block code were slow enough to constitute torture on their own.
    So we can preserve backwards compatabliity simply by including the
    former *chunk fields (renamed legacy* here) in the CRC and checking
    for the expected single-block key values.  We probably want to include
    everything in the CRC in any case except when there's an explicit
    reason omit something, so, this is cheap, just a bit obscure.
    
    At some point in the future we can phase out support for the backwards
    compatible values, but there's no particular hurry about it unless we
    want to reuse those fields for some other purpose.
---
 ks.c | 17 ++++++++++++++---
 ks.h | 13 +++++++++++--
 2 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/ks.c b/ks.c
index 665a2fd..a4e7498 100644
--- a/ks.c
+++ b/ks.c
@@ -130,6 +130,12 @@ hal_crc32_t hal_ks_block_calculate_crc(const hal_ks_block_t * const block)
     crc = hal_crc32_update(crc,  &block->header.block_type,
                            sizeof(block->header.block_type));
 
+    crc = hal_crc32_update(crc, &block->header.legacy_1,
+                           sizeof(block->header.legacy_1));
+
+    crc = hal_crc32_update(crc, &block->header.legacy_2,
+                           sizeof(block->header.legacy_2));
+
     crc = hal_crc32_update(crc,
                            block->bytes   + sizeof(hal_ks_block_header_t),
                            sizeof(*block) - sizeof(hal_ks_block_header_t));
@@ -310,11 +316,16 @@ hal_error_t hal_ks_init_common(hal_ks_t *ks)
     if (err == HAL_ERROR_KEYSTORE_BAD_CRC || err == HAL_ERROR_KEYSTORE_BAD_BLOCK_TYPE)
       block_types[i] = HAL_KS_BLOCK_TYPE_UNKNOWN;
 
-    else if (err == HAL_OK)
-      block_types[i] = hal_ks_block_get_type(block);
+    else if (err != HAL_OK)
+      return err;
+
+    else if ((block->header.legacy_1 != 0xFF || block->header.legacy_2 != 0xFF) &&
+             (block->header.legacy_1 != 0x01 || block->header.legacy_2 != 0x00))
+      block_types[i] = HAL_KS_BLOCK_TYPE_UNKNOWN;
 
     else
-      return err;
+      block_types[i] = hal_ks_block_get_type(block);
+
 
     switch (block_types[i]) {
     case HAL_KS_BLOCK_TYPE_KEY:
diff --git a/ks.h b/ks.h
index 1c09b53..b95216d 100644
--- a/ks.h
+++ b/ks.h
@@ -86,13 +86,22 @@ typedef enum {
 } hal_ks_block_status_t;
 
 /*
- * Common header for all keystore block types.
- * A few of these fields are deliberately omitted from the CRC.
+ * Common header for all keystore block types.  A few of these fields
+ * are deliberately omitted from the CRC.
+ *
+ * The legacy_1 and legacy_2 fields were used in the more complex
+ * "chunked" layout used in an earlier iteration of this keystore
+ * design, which proved more complex than it was worth.  At the
+ * moment, the only thing we do with these fields is include them in
+ * the CRC and check them for allowed values, to avoid gratuitously
+ * breaking backwards compatability with the earlier design.
  */
 
 typedef struct {
   uint8_t               block_type;
   uint8_t               block_status;
+  uint8_t               legacy_1;
+  uint8_t               legacy_2;
   hal_crc32_t           crc;
 } hal_ks_block_header_t;