drivers/auth/mbedtls/mbedtls_x509_parser.c - imx-atf - Git at Google

 /*
  * Copyright (c) 2015-2017, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */

 /*
  * X509 parser based on mbed TLS
  *
  * This module implements functions to check the integrity of a X509v3
  * certificate ASN.1 structure and extract authentication parameters from the
  * extensions field, such as an image hash or a public key.
  */

 #include <arch_helpers.h>
 #include <assert.h>
 #include <img_parser_mod.h>
 #include <mbedtls_common.h>
 #include <stddef.h>
 #include <stdint.h>
 #include <string.h>
 #include <utils.h>

 /* mbed TLS headers */
 #include <mbedtls/asn1.h>
 #include <mbedtls/oid.h>
 #include <mbedtls/platform.h>

 /* Maximum OID string length ("a.b.c.d.e.f ...") */
 #define MAX_OID_STR_LEN			64

 #define LIB_NAME	"mbed TLS X509v3"

 /* Temporary variables to speed up the authentication parameters search. These
  * variables are assigned once during the integrity check and used any time an
  * authentication parameter is requested, so we do not have to parse the image
  * again */
 static mbedtls_asn1_buf tbs;
 static mbedtls_asn1_buf v3_ext;
 static mbedtls_asn1_buf pk;
 static mbedtls_asn1_buf sig_alg;
 static mbedtls_asn1_buf signature;

 /*
  * Clear all static temporary variables.
  */
 static void clear_temp_vars(void)
 {
 #define ZERO_AND_CLEAN(x)					\
 	do {							\
 		zeromem(&x, sizeof(x));				\
 		clean_dcache_range((uintptr_t)&x, sizeof(x));	\
 	} while (0);

 	ZERO_AND_CLEAN(tbs)
 	ZERO_AND_CLEAN(v3_ext);
 	ZERO_AND_CLEAN(pk);
 	ZERO_AND_CLEAN(sig_alg);
 	ZERO_AND_CLEAN(signature);

 #undef ZERO_AND_CLEAN
 }

 /*
  * Get X509v3 extension
  *
  * Global variable 'v3_ext' must point to the extensions region
  * in the certificate. No need to check for errors since the image has passed
  * the integrity check.
  */
 static int get_ext(const char *oid, void **ext, unsigned int *ext_len)
 {
 	int oid_len;
 	size_t len;
 	unsigned char *end_ext_data, *end_ext_octet;
 	unsigned char *p;
 	const unsigned char *end;
 	char oid_str[MAX_OID_STR_LEN];
 	mbedtls_asn1_buf extn_oid;
 	int is_critical;

 	assert(oid != NULL);

 	p = v3_ext.p;
 	end = v3_ext.p + v3_ext.len;

 	mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED |
 			     MBEDTLS_ASN1_SEQUENCE);

 	while (p < end) {
 		zeromem(&extn_oid, sizeof(extn_oid));
 		is_critical = 0; /* DEFAULT FALSE */

 		mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED |
 				     MBEDTLS_ASN1_SEQUENCE);
 		end_ext_data = p + len;

 		/* Get extension ID */
 		extn_oid.tag = *p;
 		mbedtls_asn1_get_tag(&p, end, &extn_oid.len, MBEDTLS_ASN1_OID);
 		extn_oid.p = p;
 		p += extn_oid.len;

 		/* Get optional critical */
 		mbedtls_asn1_get_bool(&p, end_ext_data, &is_critical);

 		/* Extension data */
 		mbedtls_asn1_get_tag(&p, end_ext_data, &len,
 				     MBEDTLS_ASN1_OCTET_STRING);
 		end_ext_octet = p + len;

 		/* Detect requested extension */
 		oid_len = mbedtls_oid_get_numeric_string(oid_str,
 							 MAX_OID_STR_LEN,
 							 &extn_oid);
 		if (oid_len == MBEDTLS_ERR_OID_BUF_TOO_SMALL) {
 			return IMG_PARSER_ERR;
 		}
 		if ((oid_len == strlen(oid_str)) && !strcmp(oid, oid_str)) {
 			*ext = (void *)p;
 			*ext_len = (unsigned int)len;
 			return IMG_PARSER_OK;
 		}

 		/* Next */
 		p = end_ext_octet;
 	}

 	return IMG_PARSER_ERR_NOT_FOUND;
 }


 /*
  * Check the integrity of the certificate ASN.1 structure.
  *
  * Extract the relevant data that will be used later during authentication.
  *
  * This function doesn't clear the static variables located on the top of this
  * file in case of an error. It is only called from check_integrity(), which
  * performs the cleanup if necessary.
  */
 static int cert_parse(void *img, unsigned int img_len)
 {
 	int ret, is_critical;
 	size_t len;
 	unsigned char *p, *end, *crt_end;
 	mbedtls_asn1_buf sig_alg1, sig_alg2;

 	p = (unsigned char *)img;
 	len = img_len;
 	end = p + len;

 	/*
 	 * Certificate  ::=  SEQUENCE  {
 	 *      tbsCertificate       TBSCertificate,
 	 *      signatureAlgorithm   AlgorithmIdentifier,
 	 *      signatureValue       BIT STRING  }
 	 */
 	ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED |
 				   MBEDTLS_ASN1_SEQUENCE);
 	if (ret != 0) {
 		return IMG_PARSER_ERR_FORMAT;
 	}

 	if (len > (size_t)(end - p)) {
 		return IMG_PARSER_ERR_FORMAT;
 	}
 	crt_end = p + len;

 	/*
 	 * TBSCertificate  ::=  SEQUENCE  {
 	 */
 	tbs.p = p;
 	ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED |
 				   MBEDTLS_ASN1_SEQUENCE);
 	if (ret != 0) {
 		return IMG_PARSER_ERR_FORMAT;
 	}
 	end = p + len;
 	tbs.len = end - tbs.p;

 	/*
 	 * Version  ::=  INTEGER  {  v1(0), v2(1), v3(2)  }
 	 */
 	ret = mbedtls_asn1_get_tag(&p, end, &len,
 				   MBEDTLS_ASN1_CONTEXT_SPECIFIC |
 				   MBEDTLS_ASN1_CONSTRUCTED | 0);
 	if (ret != 0) {
 		return IMG_PARSER_ERR_FORMAT;
 	}
 	p += len;

 	/*
 	 * CertificateSerialNumber  ::=  INTEGER
 	 */
 	ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_INTEGER);
 	if (ret != 0) {
 		return IMG_PARSER_ERR_FORMAT;
 	}
 	p += len;

 	/*
 	 * signature            AlgorithmIdentifier
 	 */
 	sig_alg1.p = p;
 	ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED |
 				   MBEDTLS_ASN1_SEQUENCE);
 	if (ret != 0) {
 		return IMG_PARSER_ERR_FORMAT;
 	}
 	if ((end - p) < 1) {
 		return IMG_PARSER_ERR_FORMAT;
 	}
 	sig_alg1.len = (p + len) - sig_alg1.p;
 	p += len;

 	/*
 	 * issuer               Name
 	 */
 	ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED |
 				   MBEDTLS_ASN1_SEQUENCE);
 	if (ret != 0) {
 		return IMG_PARSER_ERR_FORMAT;
 	}
 	p += len;

 	/*
 	 * Validity ::= SEQUENCE {
 	 *      notBefore      Time,
 	 *      notAfter       Time }
 	 *
 	 */
 	ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED |
 				   MBEDTLS_ASN1_SEQUENCE);
 	if (ret != 0) {
 		return IMG_PARSER_ERR_FORMAT;
 	}
 	p += len;

 	/*
 	 * subject              Name
 	 */
 	ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED |
 				   MBEDTLS_ASN1_SEQUENCE);
 	if (ret != 0) {
 		return IMG_PARSER_ERR_FORMAT;
 	}
 	p += len;

 	/*
 	 * SubjectPublicKeyInfo
 	 */
 	pk.p = p;
 	ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED |
 				   MBEDTLS_ASN1_SEQUENCE);
 	if (ret != 0) {
 		return IMG_PARSER_ERR_FORMAT;
 	}
 	pk.len = (p + len) - pk.p;
 	p += len;

 	/*
 	 * issuerUniqueID  [1]  IMPLICIT UniqueIdentifier OPTIONAL,
 	 */
 	ret = mbedtls_asn1_get_tag(&p, end, &len,
 				   MBEDTLS_ASN1_CONTEXT_SPECIFIC |
 				   MBEDTLS_ASN1_CONSTRUCTED | 1);
 	if (ret != 0) {
 		if (ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG) {
 			return IMG_PARSER_ERR_FORMAT;
 		}
 	} else {
 		p += len;
 	}

 	/*
 	 * subjectUniqueID [2]  IMPLICIT UniqueIdentifier OPTIONAL,
 	 */
 	ret = mbedtls_asn1_get_tag(&p, end, &len,
 				   MBEDTLS_ASN1_CONTEXT_SPECIFIC |
 				   MBEDTLS_ASN1_CONSTRUCTED | 2);
 	if (ret != 0) {
 		if (ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG) {
 			return IMG_PARSER_ERR_FORMAT;
 		}
 	} else {
 		p += len;
 	}

 	/*
 	 * extensions      [3]  EXPLICIT Extensions OPTIONAL
 	 */
 	ret = mbedtls_asn1_get_tag(&p, end, &len,
 				   MBEDTLS_ASN1_CONTEXT_SPECIFIC |
 				   MBEDTLS_ASN1_CONSTRUCTED | 3);
 	if (ret != 0) {
 		return IMG_PARSER_ERR_FORMAT;
 	}

 	/*
 	 * Extensions  ::=  SEQUENCE SIZE (1..MAX) OF Extension
 	 */
 	v3_ext.p = p;
 	ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED |
 				   MBEDTLS_ASN1_SEQUENCE);
 	if (ret != 0) {
 		return IMG_PARSER_ERR_FORMAT;
 	}
 	v3_ext.len = (p + len) - v3_ext.p;

 	/*
 	 * Check extensions integrity
 	 */
 	while (p < end) {
 		ret = mbedtls_asn1_get_tag(&p, end, &len,
 					   MBEDTLS_ASN1_CONSTRUCTED |
 					   MBEDTLS_ASN1_SEQUENCE);
 		if (ret != 0) {
 			return IMG_PARSER_ERR_FORMAT;
 		}

 		/* Get extension ID */
 		ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_OID);
 		if (ret != 0) {
 			return IMG_PARSER_ERR_FORMAT;
 		}
 		p += len;

 		/* Get optional critical */
 		ret = mbedtls_asn1_get_bool(&p, end, &is_critical);
 		if ((ret != 0) && (ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG)) {
 			return IMG_PARSER_ERR_FORMAT;
 		}

 		/* Data should be octet string type */
 		ret = mbedtls_asn1_get_tag(&p, end, &len,
 					   MBEDTLS_ASN1_OCTET_STRING);
 		if (ret != 0) {
 			return IMG_PARSER_ERR_FORMAT;
 		}
 		p += len;
 	}

 	if (p != end) {
 		return IMG_PARSER_ERR_FORMAT;
 	}

 	end = crt_end;

 	/*
 	 *  }
 	 *  -- end of TBSCertificate
 	 *
 	 *  signatureAlgorithm   AlgorithmIdentifier
 	 */
 	sig_alg2.p = p;
 	ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED |
 				   MBEDTLS_ASN1_SEQUENCE);
 	if (ret != 0) {
 		return IMG_PARSER_ERR_FORMAT;
 	}
 	if ((end - p) < 1) {
 		return IMG_PARSER_ERR_FORMAT;
 	}
 	sig_alg2.len = (p + len) - sig_alg2.p;
 	p += len;

 	/* Compare both signature algorithms */
 	if (sig_alg1.len != sig_alg2.len) {
 		return IMG_PARSER_ERR_FORMAT;
 	}
 	if (0 != memcmp(sig_alg1.p, sig_alg2.p, sig_alg1.len)) {
 		return IMG_PARSER_ERR_FORMAT;
 	}
 	memcpy(&sig_alg, &sig_alg1, sizeof(sig_alg));

 	/*
 	 * signatureValue       BIT STRING
 	 */
 	signature.p = p;
 	ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_BIT_STRING);
 	if (ret != 0) {
 		return IMG_PARSER_ERR_FORMAT;
 	}
 	signature.len = (p + len) - signature.p;
 	p += len;

 	/* Check certificate length */
 	if (p != end) {
 		return IMG_PARSER_ERR_FORMAT;
 	}

 	return IMG_PARSER_OK;
 }


 /* Exported functions */

 static void init(void)
 {
 	mbedtls_init();
 }

 /*
  * Wrapper for cert_parse() that clears the static variables used by it in case
  * of an error.
  */
 static int check_integrity(void *img, unsigned int img_len)
 {
 	int rc = cert_parse(img, img_len);

 	if (rc != IMG_PARSER_OK)
 		clear_temp_vars();

 	return rc;
 }

 /*
  * Extract an authentication parameter from an X509v3 certificate
  *
  * This function returns a pointer to the extracted data and its length.
  * Depending on the type of parameter, a pointer to the data stored in the
  * certificate may be returned (i.e. an octet string containing a hash). Other
  * data may need to be copied and formatted (i.e. integers). In the later case,
  * a buffer of the correct type needs to be statically allocated, filled and
  * returned.
  */
 static int get_auth_param(const auth_param_type_desc_t *type_desc,
 		void *img, unsigned int img_len,
 		void **param, unsigned int *param_len)
 {
 	int rc = IMG_PARSER_OK;

 	/* We do not use img because the check_integrity function has already
 	 * extracted the relevant data (v3_ext, pk, sig_alg, etc) */

 	switch (type_desc->type) {
 	case AUTH_PARAM_RAW_DATA:
 		/* Data to be signed */
 		*param = (void *)tbs.p;
 		*param_len = (unsigned int)tbs.len;
 		break;
 	case AUTH_PARAM_HASH:
 	case AUTH_PARAM_NV_CTR:
 		/* All these parameters are included as X509v3 extensions */
 		rc = get_ext(type_desc->cookie, param, param_len);
 		break;
 	case AUTH_PARAM_PUB_KEY:
 		if (type_desc->cookie != 0) {
 			/* Get public key from extension */
 			rc = get_ext(type_desc->cookie, param, param_len);
 		} else {
 			/* Get the subject public key */
 			*param = (void *)pk.p;
 			*param_len = (unsigned int)pk.len;
 		}
 		break;
 	case AUTH_PARAM_SIG_ALG:
 		/* Get the certificate signature algorithm */
 		*param = (void *)sig_alg.p;
 		*param_len = (unsigned int)sig_alg.len;
 		break;
 	case AUTH_PARAM_SIG:
 		/* Get the certificate signature */
 		*param = (void *)signature.p;
 		*param_len = (unsigned int)signature.len;
 		break;
 	default:
 		rc = IMG_PARSER_ERR_NOT_FOUND;
 		break;
 	}

 	return rc;
 }

 REGISTER_IMG_PARSER_LIB(IMG_CERT, LIB_NAME, init, \
 		       check_integrity, get_auth_param);
	/*
	* Copyright (c) 2015-2017, ARM Limited and Contributors. All rights reserved.
	*
	* SPDX-License-Identifier: BSD-3-Clause
	*/

	/*
	* X509 parser based on mbed TLS
	*
	* This module implements functions to check the integrity of a X509v3
	* certificate ASN.1 structure and extract authentication parameters from the
	* extensions field, such as an image hash or a public key.
	*/

	#include <arch_helpers.h>
	#include <assert.h>
	#include <img_parser_mod.h>
	#include <mbedtls_common.h>
	#include <stddef.h>
	#include <stdint.h>
	#include <string.h>
	#include <utils.h>

	/* mbed TLS headers */
	#include <mbedtls/asn1.h>
	#include <mbedtls/oid.h>
	#include <mbedtls/platform.h>

	/* Maximum OID string length ("a.b.c.d.e.f ...") */
	#define MAX_OID_STR_LEN 64

	#define LIB_NAME "mbed TLS X509v3"

	/* Temporary variables to speed up the authentication parameters search. These
	* variables are assigned once during the integrity check and used any time an
	* authentication parameter is requested, so we do not have to parse the image
	* again */
	static mbedtls_asn1_buf tbs;
	static mbedtls_asn1_buf v3_ext;
	static mbedtls_asn1_buf pk;
	static mbedtls_asn1_buf sig_alg;
	static mbedtls_asn1_buf signature;

	/*
	* Clear all static temporary variables.
	*/
	static void clear_temp_vars(void)
	{
	#define ZERO_AND_CLEAN(x) \
	do { \
	zeromem(&x, sizeof(x)); \
	clean_dcache_range((uintptr_t)&x, sizeof(x)); \
	} while (0);

	ZERO_AND_CLEAN(tbs)
	ZERO_AND_CLEAN(v3_ext);
	ZERO_AND_CLEAN(pk);
	ZERO_AND_CLEAN(sig_alg);
	ZERO_AND_CLEAN(signature);

	#undef ZERO_AND_CLEAN
	}

	/*
	* Get X509v3 extension
	*
	* Global variable 'v3_ext' must point to the extensions region
	* in the certificate. No need to check for errors since the image has passed
	* the integrity check.
	*/
	static int get_ext(const char oid, void ext, unsigned int ext_len)
	{
	int oid_len;
	size_t len;
	unsigned char end_ext_data, end_ext_octet;
	unsigned char *p;
	const unsigned char *end;
	char oid_str[MAX_OID_STR_LEN];
	mbedtls_asn1_buf extn_oid;
	int is_critical;

	assert(oid != NULL);

	p = v3_ext.p;
	end = v3_ext.p + v3_ext.len;

	mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED \|
	MBEDTLS_ASN1_SEQUENCE);

	while (p < end) {
	zeromem(&extn_oid, sizeof(extn_oid));
	is_critical = 0; /* DEFAULT FALSE */

	mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED \|
	MBEDTLS_ASN1_SEQUENCE);
	end_ext_data = p + len;

	/* Get extension ID */
	extn_oid.tag = *p;
	mbedtls_asn1_get_tag(&p, end, &extn_oid.len, MBEDTLS_ASN1_OID);
	extn_oid.p = p;
	p += extn_oid.len;

	/* Get optional critical */
	mbedtls_asn1_get_bool(&p, end_ext_data, &is_critical);

	/* Extension data */
	mbedtls_asn1_get_tag(&p, end_ext_data, &len,
	MBEDTLS_ASN1_OCTET_STRING);
	end_ext_octet = p + len;

	/* Detect requested extension */
	oid_len = mbedtls_oid_get_numeric_string(oid_str,
	MAX_OID_STR_LEN,
	&extn_oid);
	if (oid_len == MBEDTLS_ERR_OID_BUF_TOO_SMALL) {
	return IMG_PARSER_ERR;
	}
	if ((oid_len == strlen(oid_str)) && !strcmp(oid, oid_str)) {
	ext = (void )p;
	*ext_len = (unsigned int)len;
	return IMG_PARSER_OK;
	}

	/* Next */
	p = end_ext_octet;
	}

	return IMG_PARSER_ERR_NOT_FOUND;
	}


	/*
	* Check the integrity of the certificate ASN.1 structure.
	*
	* Extract the relevant data that will be used later during authentication.
	*
	* This function doesn't clear the static variables located on the top of this
	* file in case of an error. It is only called from check_integrity(), which
	* performs the cleanup if necessary.
	*/
	static int cert_parse(void *img, unsigned int img_len)
	{
	int ret, is_critical;
	size_t len;
	unsigned char p, end, *crt_end;
	mbedtls_asn1_buf sig_alg1, sig_alg2;

	p = (unsigned char *)img;
	len = img_len;
	end = p + len;

	/*
	* Certificate ::= SEQUENCE {
	* tbsCertificate TBSCertificate,
	* signatureAlgorithm AlgorithmIdentifier,
	* signatureValue BIT STRING }
	*/
	ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED \|
	MBEDTLS_ASN1_SEQUENCE);
	if (ret != 0) {
	return IMG_PARSER_ERR_FORMAT;
	}

	if (len > (size_t)(end - p)) {
	return IMG_PARSER_ERR_FORMAT;
	}
	crt_end = p + len;

	/*
	* TBSCertificate ::= SEQUENCE {
	*/
	tbs.p = p;
	ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED \|
	MBEDTLS_ASN1_SEQUENCE);
	if (ret != 0) {
	return IMG_PARSER_ERR_FORMAT;
	}
	end = p + len;
	tbs.len = end - tbs.p;

	/*
	* Version ::= INTEGER { v1(0), v2(1), v3(2) }
	*/
	ret = mbedtls_asn1_get_tag(&p, end, &len,
	MBEDTLS_ASN1_CONTEXT_SPECIFIC \|
	MBEDTLS_ASN1_CONSTRUCTED \| 0);
	if (ret != 0) {
	return IMG_PARSER_ERR_FORMAT;
	}
	p += len;

	/*
	* CertificateSerialNumber ::= INTEGER
	*/
	ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_INTEGER);
	if (ret != 0) {
	return IMG_PARSER_ERR_FORMAT;
	}
	p += len;

	/*
	* signature AlgorithmIdentifier
	*/
	sig_alg1.p = p;
	ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED \|
	MBEDTLS_ASN1_SEQUENCE);
	if (ret != 0) {
	return IMG_PARSER_ERR_FORMAT;
	}
	if ((end - p) < 1) {
	return IMG_PARSER_ERR_FORMAT;
	}
	sig_alg1.len = (p + len) - sig_alg1.p;
	p += len;

	/*
	* issuer Name
	*/
	ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED \|
	MBEDTLS_ASN1_SEQUENCE);
	if (ret != 0) {
	return IMG_PARSER_ERR_FORMAT;
	}
	p += len;

	/*
	* Validity ::= SEQUENCE {
	* notBefore Time,
	* notAfter Time }
	*
	*/
	ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED \|
	MBEDTLS_ASN1_SEQUENCE);
	if (ret != 0) {
	return IMG_PARSER_ERR_FORMAT;
	}
	p += len;

	/*
	* subject Name
	*/
	ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED \|
	MBEDTLS_ASN1_SEQUENCE);
	if (ret != 0) {
	return IMG_PARSER_ERR_FORMAT;
	}
	p += len;

	/*
	* SubjectPublicKeyInfo
	*/
	pk.p = p;
	ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED \|
	MBEDTLS_ASN1_SEQUENCE);
	if (ret != 0) {
	return IMG_PARSER_ERR_FORMAT;
	}
	pk.len = (p + len) - pk.p;
	p += len;

	/*
	* issuerUniqueID [1] IMPLICIT UniqueIdentifier OPTIONAL,
	*/
	ret = mbedtls_asn1_get_tag(&p, end, &len,
	MBEDTLS_ASN1_CONTEXT_SPECIFIC \|
	MBEDTLS_ASN1_CONSTRUCTED \| 1);
	if (ret != 0) {
	if (ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG) {
	return IMG_PARSER_ERR_FORMAT;
	}
	} else {
	p += len;
	}

	/*
	* subjectUniqueID [2] IMPLICIT UniqueIdentifier OPTIONAL,
	*/
	ret = mbedtls_asn1_get_tag(&p, end, &len,
	MBEDTLS_ASN1_CONTEXT_SPECIFIC \|
	MBEDTLS_ASN1_CONSTRUCTED \| 2);
	if (ret != 0) {
	if (ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG) {
	return IMG_PARSER_ERR_FORMAT;
	}
	} else {
	p += len;
	}

	/*
	* extensions [3] EXPLICIT Extensions OPTIONAL
	*/
	ret = mbedtls_asn1_get_tag(&p, end, &len,
	MBEDTLS_ASN1_CONTEXT_SPECIFIC \|
	MBEDTLS_ASN1_CONSTRUCTED \| 3);
	if (ret != 0) {
	return IMG_PARSER_ERR_FORMAT;
	}

	/*
	* Extensions ::= SEQUENCE SIZE (1..MAX) OF Extension
	*/
	v3_ext.p = p;
	ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED \|
	MBEDTLS_ASN1_SEQUENCE);
	if (ret != 0) {
	return IMG_PARSER_ERR_FORMAT;
	}
	v3_ext.len = (p + len) - v3_ext.p;

	/*
	* Check extensions integrity
	*/
	while (p < end) {
	ret = mbedtls_asn1_get_tag(&p, end, &len,
	MBEDTLS_ASN1_CONSTRUCTED \|
	MBEDTLS_ASN1_SEQUENCE);
	if (ret != 0) {
	return IMG_PARSER_ERR_FORMAT;
	}

	/* Get extension ID */
	ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_OID);
	if (ret != 0) {
	return IMG_PARSER_ERR_FORMAT;
	}
	p += len;

	/* Get optional critical */
	ret = mbedtls_asn1_get_bool(&p, end, &is_critical);
	if ((ret != 0) && (ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG)) {
	return IMG_PARSER_ERR_FORMAT;
	}

	/* Data should be octet string type */
	ret = mbedtls_asn1_get_tag(&p, end, &len,
	MBEDTLS_ASN1_OCTET_STRING);
	if (ret != 0) {
	return IMG_PARSER_ERR_FORMAT;
	}
	p += len;
	}

	if (p != end) {
	return IMG_PARSER_ERR_FORMAT;
	}

	end = crt_end;

	/*
	* }
	* -- end of TBSCertificate
	*
	* signatureAlgorithm AlgorithmIdentifier
	*/
	sig_alg2.p = p;
	ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED \|
	MBEDTLS_ASN1_SEQUENCE);
	if (ret != 0) {
	return IMG_PARSER_ERR_FORMAT;
	}
	if ((end - p) < 1) {
	return IMG_PARSER_ERR_FORMAT;
	}
	sig_alg2.len = (p + len) - sig_alg2.p;
	p += len;

	/* Compare both signature algorithms */
	if (sig_alg1.len != sig_alg2.len) {
	return IMG_PARSER_ERR_FORMAT;
	}
	if (0 != memcmp(sig_alg1.p, sig_alg2.p, sig_alg1.len)) {
	return IMG_PARSER_ERR_FORMAT;
	}
	memcpy(&sig_alg, &sig_alg1, sizeof(sig_alg));

	/*
	* signatureValue BIT STRING
	*/
	signature.p = p;
	ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_BIT_STRING);
	if (ret != 0) {
	return IMG_PARSER_ERR_FORMAT;
	}
	signature.len = (p + len) - signature.p;
	p += len;

	/* Check certificate length */
	if (p != end) {
	return IMG_PARSER_ERR_FORMAT;
	}

	return IMG_PARSER_OK;
	}


	/* Exported functions */

	static void init(void)
	{
	mbedtls_init();
	}

	/*
	* Wrapper for cert_parse() that clears the static variables used by it in case
	* of an error.
	*/
	static int check_integrity(void *img, unsigned int img_len)
	{
	int rc = cert_parse(img, img_len);

	if (rc != IMG_PARSER_OK)
	clear_temp_vars();

	return rc;
	}

	/*
	* Extract an authentication parameter from an X509v3 certificate
	*
	* This function returns a pointer to the extracted data and its length.
	* Depending on the type of parameter, a pointer to the data stored in the
	* certificate may be returned (i.e. an octet string containing a hash). Other
	* data may need to be copied and formatted (i.e. integers). In the later case,
	* a buffer of the correct type needs to be statically allocated, filled and
	* returned.
	*/
	static int get_auth_param(const auth_param_type_desc_t *type_desc,
	void *img, unsigned int img_len,
	void *param, unsigned int param_len)
	{
	int rc = IMG_PARSER_OK;

	/* We do not use img because the check_integrity function has already
	* extracted the relevant data (v3_ext, pk, sig_alg, etc) */

	switch (type_desc->type) {
	case AUTH_PARAM_RAW_DATA:
	/* Data to be signed */
	param = (void )tbs.p;
	*param_len = (unsigned int)tbs.len;
	break;
	case AUTH_PARAM_HASH:
	case AUTH_PARAM_NV_CTR:
	/* All these parameters are included as X509v3 extensions */
	rc = get_ext(type_desc->cookie, param, param_len);
	break;
	case AUTH_PARAM_PUB_KEY:
	if (type_desc->cookie != 0) {
	/* Get public key from extension */
	rc = get_ext(type_desc->cookie, param, param_len);
	} else {
	/* Get the subject public key */
	param = (void )pk.p;
	*param_len = (unsigned int)pk.len;
	}
	break;
	case AUTH_PARAM_SIG_ALG:
	/* Get the certificate signature algorithm */
	param = (void )sig_alg.p;
	*param_len = (unsigned int)sig_alg.len;
	break;
	case AUTH_PARAM_SIG:
	/* Get the certificate signature */
	param = (void )signature.p;
	*param_len = (unsigned int)signature.len;
	break;
	default:
	rc = IMG_PARSER_ERR_NOT_FOUND;
	break;
	}

	return rc;
	}

	REGISTER_IMG_PARSER_LIB(IMG_CERT, LIB_NAME, init, \
	check_integrity, get_auth_param);