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@@ -0,0 +1,306 @@
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+// SPDX-License-Identifier: GPL-2.0+
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+/*
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+ * ECDSA image signing implementation using libcrypto backend
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+ *
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+ * The signature is a binary representation of the (R, S) points, padded to the
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+ * key size. The signature will be (2 * key_size_bits) / 8 bytes.
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+ *
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+ * Deviations from behavior of RSA equivalent:
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+ * - Verification uses private key. This is not technically required, but a
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+ * limitation on how clumsy the openssl API is to use.
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+ * - Handling of keys and key paths:
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+ * - The '-K' key directory option must contain path to the key file,
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+ * instead of the key directory.
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+ * - No assumptions are made about the file extension of the key
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+ * - The 'key-name-hint' property is only used for naming devicetree nodes,
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+ * but is not used for looking up keys on the filesystem.
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+ *
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+ * Copyright (c) 2020,2021, Alexandru Gagniuc <mr.nuke.me@gmail.com>
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+ */
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+
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+#include <u-boot/ecdsa.h>
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+#include <u-boot/fdt-libcrypto.h>
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+#include <openssl/ssl.h>
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+#include <openssl/ec.h>
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+#include <openssl/bn.h>
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+
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+/* Image signing context for openssl-libcrypto */
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+struct signer {
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+ EVP_PKEY *evp_key; /* Pointer to EVP_PKEY object */
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+ EC_KEY *ecdsa_key; /* Pointer to EC_KEY object */
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+ void *hash; /* Pointer to hash used for verification */
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+ void *signature; /* Pointer to output signature. Do not free()!*/
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+};
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+
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+static int alloc_ctx(struct signer *ctx, const struct image_sign_info *info)
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+{
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+ memset(ctx, 0, sizeof(*ctx));
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+
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+ if (!OPENSSL_init_ssl(0, NULL)) {
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+ fprintf(stderr, "Failure to init SSL library\n");
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+ return -1;
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+ }
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+
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+ ctx->hash = malloc(info->checksum->checksum_len);
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+ ctx->signature = malloc(info->crypto->key_len * 2);
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+
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+ if (!ctx->hash || !ctx->signature)
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+ return -ENOMEM;
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+
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+ return 0;
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+}
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+
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+static void free_ctx(struct signer *ctx)
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+{
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+ if (ctx->ecdsa_key)
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+ EC_KEY_free(ctx->ecdsa_key);
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+
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+ if (ctx->evp_key)
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+ EVP_PKEY_free(ctx->evp_key);
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+
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+ if (ctx->hash)
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+ free(ctx->hash);
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+}
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+
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+/*
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+ * Convert an ECDSA signature to raw format
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+ *
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+ * openssl DER-encodes 'binary' signatures. We want the signature in a raw
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+ * (R, S) point pair. So we have to dance a bit.
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+ */
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+static void ecdsa_sig_encode_raw(void *buf, const ECDSA_SIG *sig, size_t order)
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+{
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+ int point_bytes = order;
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+ const BIGNUM *r, *s;
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+ uintptr_t s_buf;
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+
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+ ECDSA_SIG_get0(sig, &r, &s);
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+ s_buf = (uintptr_t)buf + point_bytes;
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+ BN_bn2binpad(r, buf, point_bytes);
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+ BN_bn2binpad(s, (void *)s_buf, point_bytes);
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+}
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+
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+/* Get a signature from a raw encoding */
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+static ECDSA_SIG *ecdsa_sig_from_raw(void *buf, size_t order)
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+{
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+ int point_bytes = order;
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+ uintptr_t s_buf;
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+ ECDSA_SIG *sig;
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+ BIGNUM *r, *s;
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+
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+ sig = ECDSA_SIG_new();
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+ if (!sig)
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+ return NULL;
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+
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+ s_buf = (uintptr_t)buf + point_bytes;
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+ r = BN_bin2bn(buf, point_bytes, NULL);
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+ s = BN_bin2bn((void *)s_buf, point_bytes, NULL);
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+ ECDSA_SIG_set0(sig, r, s);
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+
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+ return sig;
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+}
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+
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+/* ECDSA key size in bytes */
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+static size_t ecdsa_key_size_bytes(const EC_KEY *key)
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+{
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+ const EC_GROUP *group;
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+
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+ group = EC_KEY_get0_group(key);
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+ return EC_GROUP_order_bits(group) / 8;
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+}
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+
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+static int read_key(struct signer *ctx, const char *key_name)
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+{
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+ FILE *f = fopen(key_name, "r");
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+
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+ if (!f) {
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+ fprintf(stderr, "Can not get key file '%s'\n", key_name);
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+ return -ENOENT;
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+ }
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+
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+ ctx->evp_key = PEM_read_PrivateKey(f, NULL, NULL, NULL);
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+ fclose(f);
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+ if (!ctx->evp_key) {
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+ fprintf(stderr, "Can not read key from '%s'\n", key_name);
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+ return -EIO;
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+ }
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+
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+ if (EVP_PKEY_id(ctx->evp_key) != EVP_PKEY_EC) {
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+ fprintf(stderr, "'%s' is not an ECDSA key\n", key_name);
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+ return -EINVAL;
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+ }
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+
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+ ctx->ecdsa_key = EVP_PKEY_get1_EC_KEY(ctx->evp_key);
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+ if (!ctx->ecdsa_key)
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+ fprintf(stderr, "Can not extract ECDSA key\n");
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+
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+ return (ctx->ecdsa_key) ? 0 : -EINVAL;
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+}
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+
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+/* Prepare a 'signer' context that's ready to sign and verify. */
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+static int prepare_ctx(struct signer *ctx, const struct image_sign_info *info)
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+{
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+ const char *kname = info->keydir;
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+ int key_len_bytes, ret;
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+
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+ ret = alloc_ctx(ctx, info);
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+ if (ret)
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+ return ret;
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+
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+ ret = read_key(ctx, kname);
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+ if (ret)
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+ return ret;
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+
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+ key_len_bytes = ecdsa_key_size_bytes(ctx->ecdsa_key);
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+ if (key_len_bytes != info->crypto->key_len) {
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+ fprintf(stderr, "Expected a %u-bit key, got %u-bit key\n",
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+ info->crypto->key_len * 8, key_len_bytes * 8);
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+ return -EINVAL;
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+ }
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+
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+ return 0;
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+}
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+
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+static int do_sign(struct signer *ctx, struct image_sign_info *info,
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+ const struct image_region region[], int region_count)
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+{
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+ const struct checksum_algo *algo = info->checksum;
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+ ECDSA_SIG *sig;
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+
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+ algo->calculate(algo->name, region, region_count, ctx->hash);
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+ sig = ECDSA_do_sign(ctx->hash, algo->checksum_len, ctx->ecdsa_key);
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+
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+ ecdsa_sig_encode_raw(ctx->signature, sig, info->crypto->key_len);
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+
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+ return 0;
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+}
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+
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+static int ecdsa_check_signature(struct signer *ctx, struct image_sign_info *info)
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+{
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+ ECDSA_SIG *sig;
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+ int okay;
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+
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+ sig = ecdsa_sig_from_raw(ctx->signature, info->crypto->key_len);
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+ if (!sig)
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+ return -ENOMEM;
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+
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+ okay = ECDSA_do_verify(ctx->hash, info->checksum->checksum_len,
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+ sig, ctx->ecdsa_key);
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+ if (!okay)
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+ fprintf(stderr, "WARNING: Signature is fake news!\n");
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+
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+ ECDSA_SIG_free(sig);
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+ return !okay;
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+}
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+
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+static int do_verify(struct signer *ctx, struct image_sign_info *info,
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+ const struct image_region region[], int region_count,
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+ uint8_t *raw_sig, uint sig_len)
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+{
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+ const struct checksum_algo *algo = info->checksum;
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+
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+ if (sig_len != info->crypto->key_len * 2) {
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+ fprintf(stderr, "Signature has wrong length\n");
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+ return -EINVAL;
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+ }
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+
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+ memcpy(ctx->signature, raw_sig, sig_len);
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+ algo->calculate(algo->name, region, region_count, ctx->hash);
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+
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+ return ecdsa_check_signature(ctx, info);
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+}
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+
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+int ecdsa_sign(struct image_sign_info *info, const struct image_region region[],
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+ int region_count, uint8_t **sigp, uint *sig_len)
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+{
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+ struct signer ctx;
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+ int ret;
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+
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+ ret = prepare_ctx(&ctx, info);
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+ if (ret >= 0) {
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+ do_sign(&ctx, info, region, region_count);
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+ *sigp = ctx.signature;
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+ *sig_len = info->crypto->key_len * 2;
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+
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+ ret = ecdsa_check_signature(&ctx, info);
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+ }
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+
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+ free_ctx(&ctx);
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+ return ret;
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+}
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+
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+int ecdsa_verify(struct image_sign_info *info,
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+ const struct image_region region[], int region_count,
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+ uint8_t *sig, uint sig_len)
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+{
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+ struct signer ctx;
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+ int ret;
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+
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+ ret = prepare_ctx(&ctx, info);
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+ if (ret >= 0)
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+ ret = do_verify(&ctx, info, region, region_count, sig, sig_len);
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+
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+ free_ctx(&ctx);
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+ return ret;
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+}
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+
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+static int do_add(struct signer *ctx, void *fdt, const char *key_node_name)
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+{
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+ int signature_node, key_node, ret, key_bits;
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+ const char *curve_name;
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+ const EC_GROUP *group;
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+ const EC_POINT *point;
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+ BIGNUM *x, *y;
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+
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+ signature_node = fdt_subnode_offset(fdt, 0, FIT_SIG_NODENAME);
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+ if (signature_node < 0) {
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+ fprintf(stderr, "Could not find 'signature node: %s\n",
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+ fdt_strerror(signature_node));
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+ return signature_node;
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+ }
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+
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+ key_node = fdt_add_subnode(fdt, signature_node, key_node_name);
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+ if (key_node < 0) {
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+ fprintf(stderr, "Could not create '%s' node: %s\n",
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+ key_node_name, fdt_strerror(key_node));
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+ return key_node;
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+ }
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+
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+ group = EC_KEY_get0_group(ctx->ecdsa_key);
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+ key_bits = EC_GROUP_order_bits(group);
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+ curve_name = OBJ_nid2sn(EC_GROUP_get_curve_name(group));
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+ /* Let 'x' and 'y' memory leak by not BN_free()'ing them. */
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+ x = BN_new();
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+ y = BN_new();
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+ point = EC_KEY_get0_public_key(ctx->ecdsa_key);
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+ EC_POINT_get_affine_coordinates(group, point, x, y, NULL);
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+
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+ ret = fdt_setprop_string(fdt, key_node, "ecdsa,curve", curve_name);
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+ if (ret < 0)
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+ return ret;
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+
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+ ret = fdt_add_bignum(fdt, key_node, "ecdsa,x-point", x, key_bits);
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+ if (ret < 0)
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+ return ret;
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+
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+ ret = fdt_add_bignum(fdt, key_node, "ecdsa,y-point", y, key_bits);
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+ if (ret < 0)
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+ return ret;
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+
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+ return 0;
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+}
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+
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+int ecdsa_add_verify_data(struct image_sign_info *info, void *fdt)
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+{
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+ const char *fdt_key_name;
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+ struct signer ctx;
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+ int ret;
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+
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+ fdt_key_name = info->keyname ? info->keyname : "default-key";
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+ ret = prepare_ctx(&ctx, info);
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+ if (ret >= 0)
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+ do_add(&ctx, fdt, fdt_key_name);
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+
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+ free_ctx(&ctx);
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+ return ret;
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+}
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