diff mbox series

[Concept,10/16] tkey: Use SHA256 to obtain the disk-encryption key

Message ID 20251115185212.539268-11-sjg@u-boot.org
State New
Headers
Series Continue TKey development |

Commit Message

Simon Glass Nov. 15, 2025, 6:51 p.m. UTC 
  From: Simon Glass <simon.glass@canonical.com>

Rather than Blake2b, use SHA256 to obtain the disk-encryption key based
on the key material provided by the TKey. This matches the upcoming
disk-encryption test.

Signed-off-by: Simon Glass <simon.glass@canonical.com>
---

 drivers/misc/tkey-uclass.c | 25 ++++++++++++++++++-------
 test/cmd/tkey.c            |  4 ++--
 test/dm/tkey.c             | 18 +++++++++---------
 3 files changed, 29 insertions(+), 18 deletions(-)
diff mbox series

Patch

diff --git a/drivers/misc/tkey-uclass.c b/drivers/misc/tkey-uclass.c
index d2c4b8351fd..fad5ffd6534 100644
--- a/drivers/misc/tkey-uclass.c
+++ b/drivers/misc/tkey-uclass.c
@@ -18,6 +18,8 @@ 
 #include <linux/kernel.h>
 #include <u-boot/blake2.h>
 #include <u-boot/schedule.h>
+#include <u-boot/sha256.h>
+#include <hexdump.h>
 
 /* TKey Protocol Constants */
 #define TKEY_FRAME_HEADER_SIZE		1
@@ -670,6 +672,7 @@  int tkey_derive_disk_key(struct udevice *dev, const void *app_data,
 			 int app_size, const void *uss, int uss_size,
 			 void *disk_key, void *pubkey, void *key_hash)
 {
+	char pubkey_hex[TKEY_PUBKEY_SIZE * 2 + 1];
 	int ret;
 
 	/* Load the signer app with USS */
@@ -693,14 +696,22 @@  int tkey_derive_disk_key(struct udevice *dev, const void *app_data,
 
 	log_debug("Public key retrieved\n");
 
-	/* Derive disk encryption key from public key using BLAKE2b */
-	ret = blake2b(disk_key, 32, pubkey, 32, NULL, 0);
-	if (ret) {
-		log_debug("Failed to derive disk key (error %d)\n", ret);
-		return ret;
-	}
+	/*
+	 * Derive disk encryption key from public key using SHA256
+	 * Must match Python tkey-fde-key.py implementation which does:
+	 * hashlib.sha256(pubkey.encode()).digest()
+	 *
+	 * This converts the binary public key to hex string,
+	 * then hashes the string bytes.
+	 */
+	bin2hex(pubkey_hex, pubkey, TKEY_PUBKEY_SIZE);
+
+	sha256_context ctx;
+	sha256_starts(&ctx);
+	sha256_update(&ctx, (const u8 *)pubkey_hex, TKEY_PUBKEY_SIZE * 2);
+	sha256_finish(&ctx, disk_key);
 
-	log_debug("Disk encryption key derived\n");
+	log_debug("Disk encryption key derived using SHA256\n");
 
 	/* Generate verification hash if requested */
 	if (key_hash) {
diff --git a/test/cmd/tkey.c b/test/cmd/tkey.c
index 605ce070f0e..f2d52850d4e 100644
--- a/test/cmd/tkey.c
+++ b/test/cmd/tkey.c
@@ -53,8 +53,8 @@  static int cmd_test_tkey_sandbox(struct unit_test_state *uts)
 	/* Test getkey command */
 	ut_assertok(run_command("tkey getkey testuss", 0));
 	ut_assert_nextline("Public Key: 505152535455565758595a5b5c5d5e5f505152535455565758595a5b5c5d5e5f");
-	ut_assert_nextline("Disk Key: 228b2f6abf8be05649b2417586150bbf3e1b3f669afa1c6151ddc72957933c21");
-	ut_assert_nextline("Verification Hash: a72a46b8f8c7ff0824416ada886f62b6c2808896d71201a32814ab432c7a81cf");
+	ut_assert_nextline("Disk Key: e9b0599268ff8b083ef80dbd04be207ce9a19a60a888ccb3fe93710a0a70a34e");
+	ut_assert_nextline("Verification Hash: 8583a08d6c534e84ae81a8518071c16a8030893df05fecb84e514438591ba5ed");
 
 	/* After getkey, device should be in app mode */
 	ut_assertok(run_command("tkey fwmode", 0));
diff --git a/test/dm/tkey.c b/test/dm/tkey.c
index 9dffae66a5e..4ff5ecad7ea 100644
--- a/test/dm/tkey.c
+++ b/test/dm/tkey.c
@@ -175,19 +175,19 @@  static int dm_test_tkey_derive_disk_key(struct unit_test_state *uts)
 		0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57,
 		0x58, 0x59, 0x5a, 0x5b, 0x5c, 0x5d, 0x5e, 0x5f,
 	};
-	/* Expected disk key: BLAKE2b(pubkey) */
+	/* Expected disk key: SHA256(pubkey) - from emulator */
 	const u8 expected_disk_key[TKEY_DISK_KEY_SIZE] = {
-		0x22, 0x8b, 0x2f, 0x6a, 0xbf, 0x8b, 0xe0, 0x56,
-		0x49, 0xb2, 0x41, 0x75, 0x86, 0x15, 0x0b, 0xbf,
-		0x3e, 0x1b, 0x3f, 0x66, 0x9a, 0xfa, 0x1c, 0x61,
-		0x51, 0xdd, 0xc7, 0x29, 0x57, 0x93, 0x3c, 0x21,
+		0xe9, 0xb0, 0x59, 0x92, 0x68, 0xff, 0x8b, 0x08,
+		0x3e, 0xf8, 0x0d, 0xbd, 0x04, 0xbe, 0x20, 0x7c,
+		0xe9, 0xa1, 0x9a, 0x60, 0xa8, 0x88, 0xcc, 0xb3,
+		0xfe, 0x93, 0x71, 0x0a, 0x0a, 0x70, 0xa3, 0x4e,
 	};
 	/* Expected key hash: BLAKE2b(disk_key) */
 	const u8 expected_key_hash[TKEY_HASH_SIZE] = {
-		0xa7, 0x2a, 0x46, 0xb8, 0xf8, 0xc7, 0xff, 0x08,
-		0x24, 0x41, 0x6a, 0xda, 0x88, 0x6f, 0x62, 0xb6,
-		0xc2, 0x80, 0x88, 0x96, 0xd7, 0x12, 0x01, 0xa3,
-		0x28, 0x14, 0xab, 0x43, 0x2c, 0x7a, 0x81, 0xcf,
+		0x85, 0x83, 0xa0, 0x8d, 0x6c, 0x53, 0x4e, 0x84,
+		0xae, 0x81, 0xa8, 0x51, 0x80, 0x71, 0xc1, 0x6a,
+		0x80, 0x30, 0x89, 0x3d, 0xf0, 0x5f, 0xec, 0xb8,
+		0x4e, 0x51, 0x44, 0x38, 0x59, 0x1b, 0xa5, 0xed,
 	};
 	struct udevice *dev;
 	u8 dummy_app[128];