drivers/auth/mbedtls/mbedtls_crypto.c - filogic/atf - Gitiles

 /*
  * Copyright (c) 2015-2023, Arm Limited and Contributors. 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 <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"

 #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 */

 /*
  * 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
  * }
  */

 /*
  * Initialize the library and export the descriptor
  */
 static void init(void)
 {
 	/* Initialize mbed TLS */
 	mbedtls_init();
 }

 #if CRYPTO_SUPPORT == CRYPTO_AUTH_VERIFY_ONLY || \
 CRYPTO_SUPPORT == CRYPTO_AUTH_VERIFY_AND_HASH_CALC
 /*
  * 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;
 	mbedtls_pk_context pk = {0};
 	int rc;
 	void *sig_opts = NULL;
 	const mbedtls_md_info_t *md_info;
 	unsigned char *p, *end;
 	unsigned char hash[MBEDTLS_MD_MAX_SIZE];

 	/* 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;
 	}

 	/* Parse the public key */
 	mbedtls_pk_init(&pk);
 	p = (unsigned char *)pk_ptr;
 	end = (unsigned char *)(p + pk_len);
 	rc = mbedtls_pk_parse_subpubkey(&p, end, &pk);
 	if (rc != 0) {
 		rc = CRYPTO_ERR_SIGNATURE;
 		goto end2;
 	}

 	/* 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 end1;
 	}
 	signature.p = p;

 	/* Calculate the hash of the data */
 	md_info = mbedtls_md_info_from_type(md_alg);
 	if (md_info == NULL) {
 		rc = CRYPTO_ERR_SIGNATURE;
 		goto end1;
 	}
 	p = (unsigned char *)data_ptr;
 	rc = mbedtls_md(md_info, p, data_len, hash);
 	if (rc != 0) {
 		rc = CRYPTO_ERR_SIGNATURE;
 		goto end1;
 	}

 	/* Verify the signature */
 	rc = mbedtls_pk_verify_ext(pk_alg, sig_opts, &pk, md_alg, hash,
 			mbedtls_md_get_size(md_info),
 			signature.p, signature.len);
 	if (rc != 0) {
 		rc = CRYPTO_ERR_SIGNATURE;
 		goto end1;
 	}

 	/* Signature verification success */
 	rc = CRYPTO_SUCCESS;

 end1:
 	mbedtls_pk_free(&pk);
 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;
 	const mbedtls_md_info_t *md_info;
 	unsigned char *p, *end, *hash;
 	unsigned char data_hash[MBEDTLS_MD_MAX_SIZE];
 	size_t len;
 	int rc;

 	/*
 	 * 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;
 	}

 	rc = mbedtls_oid_get_md_alg(&hash_oid, &md_alg);
 	if (rc != 0) {
 		return CRYPTO_ERR_HASH;
 	}

 	md_info = mbedtls_md_info_from_type(md_alg);
 	if (md_info == NULL) {
 		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;
 	}

 	/* Length of hash must match the algorithm's size */
 	if (len != mbedtls_md_get_size(md_info)) {
 		return CRYPTO_ERR_HASH;
 	}
 	hash = p;

 	/* Calculate the hash of the data */
 	p = (unsigned char *)data_ptr;
 	rc = mbedtls_md(md_info, p, data_len, data_hash);
 	if (rc != 0) {
 		return CRYPTO_ERR_HASH;
 	}

 	/* Compare values */
 	rc = memcmp(data_hash, hash, mbedtls_md_get_size(md_info));
 	if (rc != 0) {
 		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])
 {
 	const mbedtls_md_info_t *md_info;

 	md_info = mbedtls_md_info_from_type(md_type(md_algo));
 	if (md_info == NULL) {
 		return CRYPTO_ERR_HASH;
 	}

 	/*
 	 * 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.
 	 */
 	return mbedtls_md(md_info, data_ptr, data_len, output);
 }
 #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 */
	/*
	* Copyright (c) 2015-2023, Arm Limited and Contributors. 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 <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"

	#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 */

	/*
	* 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
	* }
	*/

	/*
	* Initialize the library and export the descriptor
	*/
	static void init(void)
	{
	/* Initialize mbed TLS */
	mbedtls_init();
	}

	#if CRYPTO_SUPPORT == CRYPTO_AUTH_VERIFY_ONLY \|\| \
	CRYPTO_SUPPORT == CRYPTO_AUTH_VERIFY_AND_HASH_CALC
	/*
	* 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;
	mbedtls_pk_context pk = {0};
	int rc;
	void *sig_opts = NULL;
	const mbedtls_md_info_t *md_info;
	unsigned char p, end;
	unsigned char hash[MBEDTLS_MD_MAX_SIZE];

	/* 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;
	}

	/* Parse the public key */
	mbedtls_pk_init(&pk);
	p = (unsigned char *)pk_ptr;
	end = (unsigned char *)(p + pk_len);
	rc = mbedtls_pk_parse_subpubkey(&p, end, &pk);
	if (rc != 0) {
	rc = CRYPTO_ERR_SIGNATURE;
	goto end2;
	}

	/* 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 end1;
	}
	signature.p = p;

	/* Calculate the hash of the data */
	md_info = mbedtls_md_info_from_type(md_alg);
	if (md_info == NULL) {
	rc = CRYPTO_ERR_SIGNATURE;
	goto end1;
	}
	p = (unsigned char *)data_ptr;
	rc = mbedtls_md(md_info, p, data_len, hash);
	if (rc != 0) {
	rc = CRYPTO_ERR_SIGNATURE;
	goto end1;
	}

	/* Verify the signature */
	rc = mbedtls_pk_verify_ext(pk_alg, sig_opts, &pk, md_alg, hash,
	mbedtls_md_get_size(md_info),
	signature.p, signature.len);
	if (rc != 0) {
	rc = CRYPTO_ERR_SIGNATURE;
	goto end1;
	}

	/* Signature verification success */
	rc = CRYPTO_SUCCESS;

	end1:
	mbedtls_pk_free(&pk);
	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;
	const mbedtls_md_info_t *md_info;
	unsigned char p, end, *hash;
	unsigned char data_hash[MBEDTLS_MD_MAX_SIZE];
	size_t len;
	int rc;

	/*
	* 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;
	}

	rc = mbedtls_oid_get_md_alg(&hash_oid, &md_alg);
	if (rc != 0) {
	return CRYPTO_ERR_HASH;
	}

	md_info = mbedtls_md_info_from_type(md_alg);
	if (md_info == NULL) {
	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;
	}

	/* Length of hash must match the algorithm's size */
	if (len != mbedtls_md_get_size(md_info)) {
	return CRYPTO_ERR_HASH;
	}
	hash = p;

	/* Calculate the hash of the data */
	p = (unsigned char *)data_ptr;
	rc = mbedtls_md(md_info, p, data_len, data_hash);
	if (rc != 0) {
	return CRYPTO_ERR_HASH;
	}

	/* Compare values */
	rc = memcmp(data_hash, hash, mbedtls_md_get_size(md_info));
	if (rc != 0) {
	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])
	{
	const mbedtls_md_info_t *md_info;

	md_info = mbedtls_md_info_from_type(md_type(md_algo));
	if (md_info == NULL) {
	return CRYPTO_ERR_HASH;
	}

	/*
	* 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.
	*/
	return mbedtls_md(md_info, data_ptr, data_len, output);
	}
	#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 */