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boot: arm-trusted-firmware-microchipsw: stabilize cert metadata
Use SOURCE_DATE_EPOCH for X.509 validity and hash the unsigned certificate fields to derive stable serial numbers. The hash includes payload extensions, so changed firmware gets a new serial. Retain the existing behavior when the variable is unset and reject invalid values. ECDSA signatures remain nondeterministic. Signed-off-by: Robert Marko <robert.marko@sartura.hr>
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@@ -1,7 +1,7 @@
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include $(TOPDIR)/rules.mk
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PKG_NAME:=arm-trusted-firmware-microchipsw
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PKG_RELEASE:=3
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PKG_RELEASE:=4
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PKG_SOURCE_PROTO:=git
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PKG_SOURCE_URL=https://github.com/microchip-ung/arm-trusted-firmware.git
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+173
@@ -0,0 +1,173 @@
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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Robert Marko <robert.marko@sartura.hr>
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Date: Mon, 12 Oct 2026 19:21:27 +0200
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Subject: [PATCH] cert_create: honour SOURCE_DATE_EPOCH for metadata
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Use SOURCE_DATE_EPOCH for certificate validity and derive serial numbers
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from stable certificate fields. Changes to authenticated payload hashes
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then change the serial, while repeated builds keep it stable.
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Keep the existing behaviour when SOURCE_DATE_EPOCH is not set and reject
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malformed values.
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Signed-off-by: Robert Marko <robert.marko@sartura.hr>
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---
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--- a/tools/cert_create/src/cert.c
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+++ b/tools/cert_create/src/cert.c
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@@ -4,9 +4,11 @@
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* SPDX-License-Identifier: BSD-3-Clause
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*/
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+#include <errno.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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+#include <time.h>
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#include <openssl/conf.h>
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#include <openssl/err.h>
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@@ -66,6 +68,84 @@ error:
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return ret;
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}
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+
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+/* Return 0 when unset, 1 for a valid epoch, and -1 for an invalid value. */
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+static int source_date_epoch(time_t *epoch)
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+{
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+ const char *value = getenv("SOURCE_DATE_EPOCH");
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+ char *end;
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+ long long seconds;
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+
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+ if (value == NULL) {
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+ return 0;
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+ }
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+ errno = 0;
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+ seconds = strtoll(value, &end, 10);
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+ if (value == end || *end != '\0' || errno != 0 || seconds < 0 ||
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+ (long long)(time_t)seconds != seconds) {
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+ ERROR("Invalid SOURCE_DATE_EPOCH: %s\n", value);
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+ return -1;
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+ }
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+ *epoch = (time_t)seconds;
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+ return 1;
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+}
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+
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+/* Feed one DER-encoded field into the serial digest and release its buffer. */
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+static int digest_der(EVP_MD_CTX *ctx, int len, unsigned char **der)
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+{
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+ int ok = len > 0 && *der != NULL && EVP_DigestUpdate(ctx, *der, len);
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+
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+ OPENSSL_free(*der);
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+ *der = NULL;
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+ return ok;
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+}
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+
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+/* Hash the unsigned certificate fields to derive a positive serial. */
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+static int deterministic_serial(X509 *x, EVP_PKEY *pkey)
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+{
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+ EVP_MD_CTX *ctx = NULL;
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+ unsigned char digest[EVP_MAX_MD_SIZE];
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+ unsigned char *der = NULL;
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+ unsigned int digest_len;
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+ BIGNUM *bn = NULL;
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+ ASN1_INTEGER *serial = NULL;
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+ int ok = 0;
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+
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+ ctx = EVP_MD_CTX_create();
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+ if (ctx == NULL || !EVP_DigestInit_ex(ctx, EVP_sha256(), NULL)) {
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+ goto out;
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+ }
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+ if (!digest_der(ctx, i2d_X509_NAME(X509_get_issuer_name(x), &der), &der) ||
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+ !digest_der(ctx, i2d_X509_NAME(X509_get_subject_name(x), &der), &der) ||
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+ !digest_der(ctx, i2d_ASN1_TIME(X509_get_notBefore(x), &der), &der) ||
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+ !digest_der(ctx, i2d_ASN1_TIME(X509_get_notAfter(x), &der), &der) ||
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+ !digest_der(ctx, i2d_PUBKEY(pkey, &der), &der) ||
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+ !digest_der(ctx, i2d_X509_EXTENSIONS(
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+ (X509_EXTENSIONS *)X509_get0_extensions(x), &der), &der) ||
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+ !EVP_DigestFinal_ex(ctx, digest, &digest_len) ||
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+ digest_len < 20) {
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+ goto out;
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+ }
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+
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+ /* RFC 5280 requires a positive serial of at most 20 octets. */
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+ digest[0] = (digest[0] & 0x7f) | 0x01;
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+ bn = BN_bin2bn(digest, 20, NULL);
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+ if (bn == NULL) {
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+ goto out;
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+ }
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+ serial = BN_to_ASN1_INTEGER(bn, NULL);
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+ if (serial == NULL || !X509_set_serialNumber(x, serial)) {
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+ goto out;
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+ }
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+ ok = 1;
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+out:
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+ OPENSSL_free(der);
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+ ASN1_INTEGER_free(serial);
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+ BN_free(bn);
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+ EVP_MD_CTX_destroy(ctx);
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+ return ok;
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+}
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+
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const EVP_MD *get_digest(int alg)
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{
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switch (alg) {
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@@ -215,7 +295,8 @@ int cert_new(
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X509_NAME *name;
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ASN1_INTEGER *sno;
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int i, num, rc = 0;
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- int fb, attempt;
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+ int fb, attempt, epoch_set;
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+ time_t epoch;
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/* Create the certificate structure */
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x = X509_new();
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@@ -242,14 +323,19 @@ int cert_new(
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/* x509.v3 */
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X509_set_version(x, 2);
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- /* Random serial number */
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- sno = ASN1_INTEGER_new();
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- rand_serial(NULL, sno);
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- X509_set_serialNumber(x, sno);
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- ASN1_INTEGER_free(sno);
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-
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- X509_gmtime_adj(X509_get_notBefore(x), 0);
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- X509_gmtime_adj(X509_get_notAfter(x), (long)60*60*24*days);
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+ epoch_set = source_date_epoch(&epoch);
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+ if (epoch_set < 0) {
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+ goto END;
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+ }
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+ if (epoch_set) {
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+ if (ASN1_TIME_adj(X509_get_notBefore(x), epoch, 0, 0) == NULL ||
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+ ASN1_TIME_adj(X509_get_notAfter(x), epoch, days, 0) == NULL) {
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+ goto END;
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+ }
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+ } else {
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+ X509_gmtime_adj(X509_get_notBefore(x), 0);
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+ X509_gmtime_adj(X509_get_notAfter(x), (long)60*60*24*days);
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+ }
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X509_set_pubkey(x, pkey);
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/* Subject name */
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@@ -283,6 +369,21 @@ int cert_new(
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}
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}
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+ if (epoch_set) {
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+ if (!deterministic_serial(x, pkey)) {
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+ ERROR("Failed to set deterministic serial for %s\n", cert->cn);
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+ goto END;
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+ }
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+ } else {
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+ sno = ASN1_INTEGER_new();
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+ if (sno == NULL || !rand_serial(NULL, sno) ||
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+ !X509_set_serialNumber(x, sno)) {
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+ ASN1_INTEGER_free(sno);
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+ goto END;
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+ }
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+ ASN1_INTEGER_free(sno);
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+ }
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+
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/*
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* Sign the certificate with the issuer key. For ECDSA, re-sign until
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* neither signature scalar (r, s) has a leading zero byte, which the
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@@ -10,5 +10,6 @@ For a device provisioned with a private root key, supply a private directory
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containing the same filenames via TFA_KEY_DIR. The root key's public X and Y
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coordinates must have no leading zero byte because of ERR-LAN969X-001.
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Fixed keys alone do not make the FIP reproducible: cert_create still generates
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random certificate serials and ECDSA signatures and uses the current time.
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The package passes SOURCE_DATE_EPOCH to cert_create for stable certificate
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validity and serials. ECDSA signatures are still random, so the FIP is not
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yet reproducible.
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