1 files changed, 696 insertions, 0 deletions

diff --git a/drivers/auth/mbedtls/mbedtls_psa_crypto.c b/drivers/auth/mbedtls/mbedtls_psa_crypto.c
new file mode 100644
index 0000000..5891acf
--- /dev/null
+++ b/drivers/auth/mbedtls/mbedtls_psa_crypto.c
@@ -0,0 +1,696 @@
+/*
+ * Copyright (c) 2023, Arm Limited. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <assert.h>
+#include <stddef.h>
+#include <string.h>
+
+/* mbed TLS headers */
+#include <mbedtls/gcm.h>
+#include <mbedtls/md.h>
+#include <mbedtls/memory_buffer_alloc.h>
+#include <mbedtls/oid.h>
+#include <mbedtls/platform.h>
+#include <mbedtls/version.h>
+#include <mbedtls/x509.h>
+#include <psa/crypto.h>
+#include <psa/crypto_platform.h>
+#include <psa/crypto_types.h>
+#include <psa/crypto_values.h>
+
+#include <common/debug.h>
+#include <drivers/auth/crypto_mod.h>
+#include <drivers/auth/mbedtls/mbedtls_common.h>
+#include <plat/common/platform.h>
+
+#define LIB_NAME		"mbed TLS PSA"
+
+/* Maximum length of R_S pair in the ECDSA signature in bytes */
+#define MAX_ECDSA_R_S_PAIR_LEN	64U
+
+/* Size of ASN.1 length and tag in bytes*/
+#define SIZE_OF_ASN1_LEN	1U
+#define SIZE_OF_ASN1_TAG	1U
+
+#if CRYPTO_SUPPORT == CRYPTO_HASH_CALC_ONLY || \
+CRYPTO_SUPPORT == CRYPTO_AUTH_VERIFY_AND_HASH_CALC
+/*
+ * CRYPTO_MD_MAX_SIZE value is as per current stronger algorithm available
+ * so make sure that mbed TLS MD maximum size must be lesser than this.
+ */
+CASSERT(CRYPTO_MD_MAX_SIZE >= MBEDTLS_MD_MAX_SIZE,
+	assert_mbedtls_md_size_overflow);
+
+#endif /*
+	* CRYPTO_SUPPORT == CRYPTO_HASH_CALC_ONLY || \
+	* CRYPTO_SUPPORT == CRYPTO_AUTH_VERIFY_AND_HASH_CALC
+	*/
+
+static inline psa_algorithm_t mbedtls_md_psa_alg_from_type(
+						mbedtls_md_type_t md_type)
+{
+	assert((md_type == MBEDTLS_MD_SHA256) ||
+	       (md_type == MBEDTLS_MD_SHA384) ||
+	       (md_type == MBEDTLS_MD_SHA512));
+
+	return PSA_ALG_CATEGORY_HASH | (psa_algorithm_t) (md_type + 0x5);
+}
+
+/*
+ * AlgorithmIdentifier  ::=  SEQUENCE  {
+ *     algorithm               OBJECT IDENTIFIER,
+ *     parameters              ANY DEFINED BY algorithm OPTIONAL
+ * }
+ *
+ * SubjectPublicKeyInfo  ::=  SEQUENCE  {
+ *     algorithm            AlgorithmIdentifier,
+ *     subjectPublicKey     BIT STRING
+ * }
+ *
+ * DigestInfo ::= SEQUENCE {
+ *     digestAlgorithm AlgorithmIdentifier,
+ *     digest OCTET STRING
+ * }
+ */
+
+/*
+ * We pretend using an external RNG (through MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG
+ * mbedTLS config option) so we need to provide an implementation of
+ * mbedtls_psa_external_get_random(). Provide a fake one, since we do not
+ * actually have any external RNG and TF-A itself doesn't engage in
+ * cryptographic operations that demands randomness.
+ */
+psa_status_t mbedtls_psa_external_get_random(
+			mbedtls_psa_external_random_context_t *context,
+			uint8_t *output, size_t output_size,
+			size_t *output_length)
+{
+	return PSA_ERROR_INSUFFICIENT_ENTROPY;
+}
+
+/*
+ * Initialize the library and export the descriptor
+ */
+static void init(void)
+{
+	/* Initialize mbed TLS */
+	mbedtls_init();
+
+	/* Initialise PSA mbedTLS */
+	psa_status_t status = psa_crypto_init();
+
+	if (status != PSA_SUCCESS) {
+		ERROR("Failed to initialize %s crypto (%d).\n", LIB_NAME, status);
+		panic();
+	}
+
+	INFO("PSA crypto initialized successfully!\n");
+}
+
+#if CRYPTO_SUPPORT == CRYPTO_AUTH_VERIFY_ONLY || \
+CRYPTO_SUPPORT == CRYPTO_AUTH_VERIFY_AND_HASH_CALC
+
+static void construct_psa_key_alg_and_type(mbedtls_pk_type_t pk_alg,
+					   mbedtls_md_type_t md_alg,
+					   psa_ecc_family_t psa_ecc_family,
+					   psa_algorithm_t *psa_alg,
+					   psa_key_type_t *psa_key_type)
+{
+	psa_algorithm_t psa_md_alg = mbedtls_md_psa_alg_from_type(md_alg);
+
+	switch (pk_alg) {
+	case MBEDTLS_PK_RSASSA_PSS:
+		*psa_alg = PSA_ALG_RSA_PSS(psa_md_alg);
+		*psa_key_type = PSA_KEY_TYPE_RSA_PUBLIC_KEY;
+		break;
+	case MBEDTLS_PK_ECDSA:
+		*psa_alg = PSA_ALG_ECDSA(psa_md_alg);
+		*psa_key_type = PSA_KEY_TYPE_ECC_PUBLIC_KEY(psa_ecc_family);
+		break;
+	default:
+		*psa_alg = PSA_ALG_NONE;
+		*psa_key_type = PSA_KEY_TYPE_NONE;
+		break;
+	}
+}
+
+
+#if TF_MBEDTLS_KEY_ALG_ID == TF_MBEDTLS_ECDSA || \
+TF_MBEDTLS_KEY_ALG_ID == TF_MBEDTLS_RSA_AND_ECDSA
+
+/*
+ * This is a helper function to detect padding byte (if the MSB bit of the
+ * first data byte is set to 1, for example 0x80) and on detection, ignore the
+ * padded byte(0x00) and increase the buffer pointer beyond padded byte and
+ * decrease the length of the buffer by 1.
+ *
+ * On Success returns 0, error otherwise.
+ **/
+static inline int ignore_asn1_int_padding_byte(unsigned char **buf_start,
+					       size_t *buf_len)
+{
+	unsigned char *local_buf = *buf_start;
+
+	/* Check for negative number */
+	if ((local_buf[0] & 0x80U) != 0U) {
+		return -1;
+	}
+
+	if ((local_buf[0] == 0U) && (local_buf[1] > 0x7FU) &&
+	    (*buf_len > 1U)) {
+		*buf_start = &local_buf[1];
+		(*buf_len)--;
+	}
+
+	return 0;
+}
+
+/*
+ * This is a helper function that gets a pointer to the encoded ECDSA publicKey
+ * and its length (as per RFC5280) and returns corresponding decoded publicKey
+ * and its length. As well, it retrieves the family of ECC key in the PSA
+ * format.
+ *
+ * This function returns error(CRYPTO_ERR_SIGNATURE) on ASN.1 parsing failure,
+ * otherwise success(0).
+ **/
+static int get_ecdsa_pkinfo_from_asn1(unsigned char **pk_start,
+				      unsigned int *pk_len,
+				      psa_ecc_family_t *psa_ecc_family)
+{
+	mbedtls_asn1_buf alg_oid, alg_params;
+	mbedtls_ecp_group_id grp_id;
+	int rc;
+	unsigned char *pk_end;
+	size_t len;
+	size_t curve_bits;
+	unsigned char *pk_ptr = *pk_start;
+
+	pk_end = pk_ptr + *pk_len;
+	rc = mbedtls_asn1_get_tag(&pk_ptr, pk_end, &len,
+				  MBEDTLS_ASN1_CONSTRUCTED |
+				  MBEDTLS_ASN1_SEQUENCE);
+	if (rc != 0) {
+		return CRYPTO_ERR_SIGNATURE;
+	}
+
+	pk_end = pk_ptr + len;
+	rc = mbedtls_asn1_get_alg(&pk_ptr, pk_end, &alg_oid, &alg_params);
+	if (rc != 0) {
+		return CRYPTO_ERR_SIGNATURE;
+	}
+
+	if (alg_params.tag == MBEDTLS_ASN1_OID) {
+		if (mbedtls_oid_get_ec_grp(&alg_params, &grp_id) != 0) {
+			return CRYPTO_ERR_SIGNATURE;
+		}
+		*psa_ecc_family = mbedtls_ecc_group_to_psa(grp_id,
+							   &curve_bits);
+	} else {
+		return CRYPTO_ERR_SIGNATURE;
+	}
+
+	pk_end = pk_ptr + len - (alg_oid.len + alg_params.len +
+		 2 * (SIZE_OF_ASN1_LEN + SIZE_OF_ASN1_TAG));
+	rc = mbedtls_asn1_get_bitstring_null(&pk_ptr, pk_end, &len);
+	if (rc != 0) {
+		return CRYPTO_ERR_SIGNATURE;
+	}
+
+	*pk_start = pk_ptr;
+	*pk_len = len;
+
+	return rc;
+}
+
+/*
+ * Ecdsa-Sig-Value  ::=  SEQUENCE  {
+ *   r     INTEGER,
+ *   s     INTEGER
+ * }
+ *
+ * This helper function that gets a pointer to the encoded ECDSA signature and
+ * its length (as per RFC5280) and returns corresponding decoded signature
+ * (R_S pair) and its size.
+ *
+ * This function returns error(CRYPTO_ERR_SIGNATURE) on ASN.1 parsing failure,
+ * otherwise success(0).
+ **/
+static int get_ecdsa_signature_from_asn1(unsigned char *sig_ptr,
+					 size_t *sig_len,
+					 unsigned char *r_s_pair)
+{
+	int rc;
+	unsigned char *sig_end;
+	size_t len, r_len, s_len;
+
+	sig_end = sig_ptr + *sig_len;
+	rc = mbedtls_asn1_get_tag(&sig_ptr, sig_end, &len,
+				  MBEDTLS_ASN1_CONSTRUCTED |
+				  MBEDTLS_ASN1_SEQUENCE);
+	if (rc != 0) {
+		return CRYPTO_ERR_SIGNATURE;
+	}
+
+	sig_end = sig_ptr + len;
+	rc = mbedtls_asn1_get_tag(&sig_ptr, sig_end, &r_len,
+				  MBEDTLS_ASN1_INTEGER);
+	if (rc != 0) {
+		return CRYPTO_ERR_SIGNATURE;
+	}
+
+	if (ignore_asn1_int_padding_byte(&sig_ptr, &r_len) != 0) {
+		return CRYPTO_ERR_SIGNATURE;
+	}
+
+	(void)memcpy((void *)&r_s_pair[0], (const void *)sig_ptr, r_len);
+
+	sig_ptr = sig_ptr + r_len;
+	sig_end = sig_ptr + len - (r_len + (SIZE_OF_ASN1_LEN +
+		  SIZE_OF_ASN1_TAG));
+	rc = mbedtls_asn1_get_tag(&sig_ptr, sig_end, &s_len,
+				  MBEDTLS_ASN1_INTEGER);
+	if (rc != 0) {
+		return CRYPTO_ERR_SIGNATURE;
+	}
+
+	if (ignore_asn1_int_padding_byte(&sig_ptr, &s_len) != 0) {
+		return CRYPTO_ERR_SIGNATURE;
+	}
+
+	(void)memcpy((void *)&r_s_pair[r_len], (const void *)sig_ptr, s_len);
+
+	*sig_len = s_len + r_len;
+
+	return 0;
+}
+#endif /*
+	* TF_MBEDTLS_KEY_ALG_ID == TF_MBEDTLS_ECDSA || \
+	* TF_MBEDTLS_KEY_ALG_ID == TF_MBEDTLS_RSA_AND_ECDSA
+	**/
+
+/*
+ * Verify a signature.
+ *
+ * Parameters are passed using the DER encoding format following the ASN.1
+ * structures detailed above.
+ */
+static int verify_signature(void *data_ptr, unsigned int data_len,
+			    void *sig_ptr, unsigned int sig_len,
+			    void *sig_alg, unsigned int sig_alg_len,
+			    void *pk_ptr, unsigned int pk_len)
+{
+	mbedtls_asn1_buf sig_oid, sig_params;
+	mbedtls_asn1_buf signature;
+	mbedtls_md_type_t md_alg;
+	mbedtls_pk_type_t pk_alg;
+	int rc;
+	void *sig_opts = NULL;
+	unsigned char *p, *end;
+	unsigned char *local_sig_ptr;
+	size_t local_sig_len;
+	psa_ecc_family_t psa_ecc_family = 0U;
+	__unused unsigned char reformatted_sig[MAX_ECDSA_R_S_PAIR_LEN] = {0};
+
+	/* construct PSA key algo and type */
+	psa_status_t status = PSA_SUCCESS;
+	psa_key_attributes_t psa_key_attr = PSA_KEY_ATTRIBUTES_INIT;
+	psa_key_id_t psa_key_id = PSA_KEY_ID_NULL;
+	psa_key_type_t psa_key_type;
+	psa_algorithm_t psa_alg;
+
+	/* Get pointers to signature OID and parameters */
+	p = (unsigned char *)sig_alg;
+	end = (unsigned char *)(p + sig_alg_len);
+	rc = mbedtls_asn1_get_alg(&p, end, &sig_oid, &sig_params);
+	if (rc != 0) {
+		return CRYPTO_ERR_SIGNATURE;
+	}
+
+	/* Get the actual signature algorithm (MD + PK) */
+	rc = mbedtls_x509_get_sig_alg(&sig_oid, &sig_params, &md_alg, &pk_alg, &sig_opts);
+	if (rc != 0) {
+		return CRYPTO_ERR_SIGNATURE;
+	}
+
+	/* Get the signature (bitstring) */
+	p = (unsigned char *)sig_ptr;
+	end = (unsigned char *)(p + sig_len);
+	signature.tag = *p;
+	rc = mbedtls_asn1_get_bitstring_null(&p, end, &signature.len);
+	if ((rc != 0) || ((size_t)(end - p) != signature.len)) {
+		rc = CRYPTO_ERR_SIGNATURE;
+		goto end2;
+	}
+
+	local_sig_ptr = p;
+	local_sig_len = signature.len;
+
+#if TF_MBEDTLS_KEY_ALG_ID == TF_MBEDTLS_ECDSA || \
+TF_MBEDTLS_KEY_ALG_ID == TF_MBEDTLS_RSA_AND_ECDSA
+	if (pk_alg == MBEDTLS_PK_ECDSA) {
+		rc = get_ecdsa_signature_from_asn1(local_sig_ptr,
+						   &local_sig_len,
+						   reformatted_sig);
+		if (rc != 0) {
+			goto end2;
+		}
+
+		local_sig_ptr = reformatted_sig;
+
+		rc = get_ecdsa_pkinfo_from_asn1((unsigned char **)&pk_ptr,
+						&pk_len,
+						&psa_ecc_family);
+		if (rc != 0) {
+			goto end2;
+		}
+	}
+#endif /*
+	* TF_MBEDTLS_KEY_ALG_ID == TF_MBEDTLS_ECDSA || \
+	* TF_MBEDTLS_KEY_ALG_ID == TF_MBEDTLS_RSA_AND_ECDSA
+	**/
+
+	/* Convert this pk_alg and md_alg to PSA key type and key algorithm */
+	construct_psa_key_alg_and_type(pk_alg, md_alg, psa_ecc_family,
+				       &psa_alg, &psa_key_type);
+
+
+	if ((psa_alg == PSA_ALG_NONE) || (psa_key_type == PSA_KEY_TYPE_NONE)) {
+		rc = CRYPTO_ERR_SIGNATURE;
+		goto end2;
+	}
+
+	/* filled-in key_attributes */
+	psa_set_key_algorithm(&psa_key_attr, psa_alg);
+	psa_set_key_type(&psa_key_attr, psa_key_type);
+	psa_set_key_usage_flags(&psa_key_attr, PSA_KEY_USAGE_VERIFY_MESSAGE);
+
+	/* Get the key_id using import API */
+	status = psa_import_key(&psa_key_attr,
+				pk_ptr,
+				(size_t)pk_len,
+				&psa_key_id);
+
+	if (status != PSA_SUCCESS) {
+		rc = CRYPTO_ERR_SIGNATURE;
+		goto end2;
+	}
+
+	/*
+	 * Hash calculation and Signature verification of the given data payload
+	 * is wrapped under the psa_verify_message function.
+	 */
+	status = psa_verify_message(psa_key_id, psa_alg,
+				    data_ptr, data_len,
+				    local_sig_ptr, local_sig_len);
+
+	if (status != PSA_SUCCESS) {
+		rc = CRYPTO_ERR_SIGNATURE;
+		goto end1;
+	}
+
+	/* Signature verification success */
+	rc = CRYPTO_SUCCESS;
+
+end1:
+	/*
+	 * Destroy the key if it is created successfully
+	 */
+	psa_destroy_key(psa_key_id);
+end2:
+	mbedtls_free(sig_opts);
+	return rc;
+}
+
+/*
+ * Match a hash
+ *
+ * Digest info is passed in DER format following the ASN.1 structure detailed
+ * above.
+ */
+static int verify_hash(void *data_ptr, unsigned int data_len,
+		       void *digest_info_ptr, unsigned int digest_info_len)
+{
+	mbedtls_asn1_buf hash_oid, params;
+	mbedtls_md_type_t md_alg;
+	unsigned char *p, *end, *hash;
+	size_t len;
+	int rc;
+	psa_status_t status;
+	psa_algorithm_t psa_md_alg;
+
+	/*
+	 * Digest info should be an MBEDTLS_ASN1_SEQUENCE, but padding after
+	 * it is allowed.  This is necessary to support multiple hash
+	 * algorithms.
+	 */
+	p = (unsigned char *)digest_info_ptr;
+	end = p + digest_info_len;
+	rc = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED |
+				  MBEDTLS_ASN1_SEQUENCE);
+	if (rc != 0) {
+		return CRYPTO_ERR_HASH;
+	}
+
+	end = p + len;
+
+	/* Get the hash algorithm */
+	rc = mbedtls_asn1_get_alg(&p, end, &hash_oid, &params);
+	if (rc != 0) {
+		return CRYPTO_ERR_HASH;
+	}
+
+	/* Hash should be octet string type and consume all bytes */
+	rc = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_OCTET_STRING);
+	if ((rc != 0) || ((size_t)(end - p) != len)) {
+		return CRYPTO_ERR_HASH;
+	}
+	hash = p;
+
+	rc = mbedtls_oid_get_md_alg(&hash_oid, &md_alg);
+	if (rc != 0) {
+		return CRYPTO_ERR_HASH;
+	}
+
+	/* convert the md_alg to psa_algo */
+	psa_md_alg = mbedtls_md_psa_alg_from_type(md_alg);
+
+	/* Length of hash must match the algorithm's size */
+	if (len != PSA_HASH_LENGTH(psa_md_alg)) {
+		return CRYPTO_ERR_HASH;
+	}
+
+	/*
+	 * Calculate Hash and compare it against the retrieved hash from
+	 * the certificate (one shot API).
+	 */
+	status = psa_hash_compare(psa_md_alg,
+				  data_ptr, (size_t)data_len,
+				  (const uint8_t *)hash, len);
+
+	if (status != PSA_SUCCESS) {
+		return CRYPTO_ERR_HASH;
+	}
+
+	return CRYPTO_SUCCESS;
+}
+#endif /*
+	* CRYPTO_SUPPORT == CRYPTO_AUTH_VERIFY_ONLY || \
+	* CRYPTO_SUPPORT == CRYPTO_AUTH_VERIFY_AND_HASH_CALC
+	*/
+
+#if CRYPTO_SUPPORT == CRYPTO_HASH_CALC_ONLY || \
+CRYPTO_SUPPORT == CRYPTO_AUTH_VERIFY_AND_HASH_CALC
+/*
+ * Map a generic crypto message digest algorithm to the corresponding macro used
+ * by Mbed TLS.
+ */
+static inline mbedtls_md_type_t md_type(enum crypto_md_algo algo)
+{
+	switch (algo) {
+	case CRYPTO_MD_SHA512:
+		return MBEDTLS_MD_SHA512;
+	case CRYPTO_MD_SHA384:
+		return MBEDTLS_MD_SHA384;
+	case CRYPTO_MD_SHA256:
+		return MBEDTLS_MD_SHA256;
+	default:
+		/* Invalid hash algorithm. */
+		return MBEDTLS_MD_NONE;
+	}
+}
+
+/*
+ * Calculate a hash
+ *
+ * output points to the computed hash
+ */
+static int calc_hash(enum crypto_md_algo md_algo, void *data_ptr,
+		     unsigned int data_len,
+		     unsigned char output[CRYPTO_MD_MAX_SIZE])
+{
+	size_t hash_length;
+	psa_status_t status;
+	psa_algorithm_t psa_md_alg;
+
+	/* convert the md_alg to psa_algo */
+	psa_md_alg = mbedtls_md_psa_alg_from_type(md_type(md_algo));
+
+	/*
+	 * Calculate the hash of the data, it is safe to pass the
+	 * 'output' hash buffer pointer considering its size is always
+	 * bigger than or equal to MBEDTLS_MD_MAX_SIZE.
+	 */
+	status = psa_hash_compute(psa_md_alg, data_ptr, (size_t)data_len,
+				  (uint8_t *)output, CRYPTO_MD_MAX_SIZE,
+				  &hash_length);
+	if (status != PSA_SUCCESS) {
+		return CRYPTO_ERR_HASH;
+	}
+
+	return CRYPTO_SUCCESS;
+}
+#endif /*
+	* CRYPTO_SUPPORT == CRYPTO_HASH_CALC_ONLY || \
+	* CRYPTO_SUPPORT == CRYPTO_AUTH_VERIFY_AND_HASH_CALC
+	*/
+
+#if TF_MBEDTLS_USE_AES_GCM
+/*
+ * Stack based buffer allocation for decryption operation. It could
+ * be configured to balance stack usage vs execution speed.
+ */
+#define DEC_OP_BUF_SIZE		128
+
+static int aes_gcm_decrypt(void *data_ptr, size_t len, const void *key,
+			   unsigned int key_len, const void *iv,
+			   unsigned int iv_len, const void *tag,
+			   unsigned int tag_len)
+{
+	mbedtls_gcm_context ctx;
+	mbedtls_cipher_id_t cipher = MBEDTLS_CIPHER_ID_AES;
+	unsigned char buf[DEC_OP_BUF_SIZE];
+	unsigned char tag_buf[CRYPTO_MAX_TAG_SIZE];
+	unsigned char *pt = data_ptr;
+	size_t dec_len;
+	int diff, i, rc;
+	size_t output_length __unused;
+
+	mbedtls_gcm_init(&ctx);
+
+	rc = mbedtls_gcm_setkey(&ctx, cipher, key, key_len * 8);
+	if (rc != 0) {
+		rc = CRYPTO_ERR_DECRYPTION;
+		goto exit_gcm;
+	}
+
+#if (MBEDTLS_VERSION_MAJOR < 3)
+	rc = mbedtls_gcm_starts(&ctx, MBEDTLS_GCM_DECRYPT, iv, iv_len, NULL, 0);
+#else
+	rc = mbedtls_gcm_starts(&ctx, MBEDTLS_GCM_DECRYPT, iv, iv_len);
+#endif
+	if (rc != 0) {
+		rc = CRYPTO_ERR_DECRYPTION;
+		goto exit_gcm;
+	}
+
+	while (len > 0) {
+		dec_len = MIN(sizeof(buf), len);
+
+#if (MBEDTLS_VERSION_MAJOR < 3)
+		rc = mbedtls_gcm_update(&ctx, dec_len, pt, buf);
+#else
+		rc = mbedtls_gcm_update(&ctx, pt, dec_len, buf, sizeof(buf), &output_length);
+#endif
+
+		if (rc != 0) {
+			rc = CRYPTO_ERR_DECRYPTION;
+			goto exit_gcm;
+		}
+
+		memcpy(pt, buf, dec_len);
+		pt += dec_len;
+		len -= dec_len;
+	}
+
+#if (MBEDTLS_VERSION_MAJOR < 3)
+	rc = mbedtls_gcm_finish(&ctx, tag_buf, sizeof(tag_buf));
+#else
+	rc = mbedtls_gcm_finish(&ctx, NULL, 0, &output_length, tag_buf, sizeof(tag_buf));
+#endif
+
+	if (rc != 0) {
+		rc = CRYPTO_ERR_DECRYPTION;
+		goto exit_gcm;
+	}
+
+	/* Check tag in "constant-time" */
+	for (diff = 0, i = 0; i < tag_len; i++)
+		diff |= ((const unsigned char *)tag)[i] ^ tag_buf[i];
+
+	if (diff != 0) {
+		rc = CRYPTO_ERR_DECRYPTION;
+		goto exit_gcm;
+	}
+
+	/* GCM decryption success */
+	rc = CRYPTO_SUCCESS;
+
+exit_gcm:
+	mbedtls_gcm_free(&ctx);
+	return rc;
+}
+
+/*
+ * Authenticated decryption of an image
+ */
+static int auth_decrypt(enum crypto_dec_algo dec_algo, void *data_ptr,
+			size_t len, const void *key, unsigned int key_len,
+			unsigned int key_flags, const void *iv,
+			unsigned int iv_len, const void *tag,
+			unsigned int tag_len)
+{
+	int rc;
+
+	assert((key_flags & ENC_KEY_IS_IDENTIFIER) == 0);
+
+	switch (dec_algo) {
+	case CRYPTO_GCM_DECRYPT:
+		rc = aes_gcm_decrypt(data_ptr, len, key, key_len, iv, iv_len,
+				     tag, tag_len);
+		if (rc != 0)
+			return rc;
+		break;
+	default:
+		return CRYPTO_ERR_DECRYPTION;
+	}
+
+	return CRYPTO_SUCCESS;
+}
+#endif /* TF_MBEDTLS_USE_AES_GCM */
+
+/*
+ * Register crypto library descriptor
+ */
+#if CRYPTO_SUPPORT == CRYPTO_AUTH_VERIFY_AND_HASH_CALC
+#if TF_MBEDTLS_USE_AES_GCM
+REGISTER_CRYPTO_LIB(LIB_NAME, init, verify_signature, verify_hash, calc_hash,
+		    auth_decrypt, NULL);
+#else
+REGISTER_CRYPTO_LIB(LIB_NAME, init, verify_signature, verify_hash, calc_hash,
+		    NULL, NULL);
+#endif
+#elif CRYPTO_SUPPORT == CRYPTO_AUTH_VERIFY_ONLY
+#if TF_MBEDTLS_USE_AES_GCM
+REGISTER_CRYPTO_LIB(LIB_NAME, init, verify_signature, verify_hash, NULL,
+		    auth_decrypt, NULL);
+#else
+REGISTER_CRYPTO_LIB(LIB_NAME, init, verify_signature, verify_hash, NULL,
+		    NULL, NULL);
+#endif
+#elif CRYPTO_SUPPORT == CRYPTO_HASH_CALC_ONLY
+REGISTER_CRYPTO_LIB(LIB_NAME, init, NULL, NULL, calc_hash, NULL, NULL);
+#endif /* CRYPTO_SUPPORT == CRYPTO_AUTH_VERIFY_AND_HASH_CALC */