Squashed 'lib/mbedtls/external/mbedtls/' content from commit 2ca6c285a0dd

git-subtree-dir: lib/mbedtls/external/mbedtls
git-subtree-split: 2ca6c285a0dd3f33982dd57299012dacab1ff206

1 files changed, 682 insertions, 0 deletions

diff --git a/library/x509write_crt.c b/library/x509write_crt.c
new file mode 100644
index 00000000000..72f5a10a17b
--- /dev/null
+++ b/library/x509write_crt.c
@@ -0,0 +1,682 @@
+/*
+ *  X.509 certificate writing
+ *
+ *  Copyright The Mbed TLS Contributors
+ *  SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
+ */
+/*
+ * References:
+ * - certificates: RFC 5280, updated by RFC 6818
+ * - CSRs: PKCS#10 v1.7 aka RFC 2986
+ * - attributes: PKCS#9 v2.0 aka RFC 2985
+ */
+
+#include "common.h"
+
+#if defined(MBEDTLS_X509_CRT_WRITE_C)
+
+#include "mbedtls/x509_crt.h"
+#include "x509_internal.h"
+#include "mbedtls/asn1write.h"
+#include "mbedtls/error.h"
+#include "mbedtls/oid.h"
+#include "mbedtls/platform.h"
+#include "mbedtls/platform_util.h"
+#include "mbedtls/md.h"
+
+#include <string.h>
+#include <stdint.h>
+
+#if defined(MBEDTLS_PEM_WRITE_C)
+#include "mbedtls/pem.h"
+#endif /* MBEDTLS_PEM_WRITE_C */
+
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
+#include "psa/crypto.h"
+#include "psa_util_internal.h"
+#include "mbedtls/psa_util.h"
+#endif /* MBEDTLS_USE_PSA_CRYPTO */
+
+void mbedtls_x509write_crt_init(mbedtls_x509write_cert *ctx)
+{
+    memset(ctx, 0, sizeof(mbedtls_x509write_cert));
+
+    ctx->version = MBEDTLS_X509_CRT_VERSION_3;
+}
+
+void mbedtls_x509write_crt_free(mbedtls_x509write_cert *ctx)
+{
+    mbedtls_asn1_free_named_data_list(&ctx->subject);
+    mbedtls_asn1_free_named_data_list(&ctx->issuer);
+    mbedtls_asn1_free_named_data_list(&ctx->extensions);
+
+    mbedtls_platform_zeroize(ctx, sizeof(mbedtls_x509write_cert));
+}
+
+void mbedtls_x509write_crt_set_version(mbedtls_x509write_cert *ctx,
+                                       int version)
+{
+    ctx->version = version;
+}
+
+void mbedtls_x509write_crt_set_md_alg(mbedtls_x509write_cert *ctx,
+                                      mbedtls_md_type_t md_alg)
+{
+    ctx->md_alg = md_alg;
+}
+
+void mbedtls_x509write_crt_set_subject_key(mbedtls_x509write_cert *ctx,
+                                           mbedtls_pk_context *key)
+{
+    ctx->subject_key = key;
+}
+
+void mbedtls_x509write_crt_set_issuer_key(mbedtls_x509write_cert *ctx,
+                                          mbedtls_pk_context *key)
+{
+    ctx->issuer_key = key;
+}
+
+int mbedtls_x509write_crt_set_subject_name(mbedtls_x509write_cert *ctx,
+                                           const char *subject_name)
+{
+    return mbedtls_x509_string_to_names(&ctx->subject, subject_name);
+}
+
+int mbedtls_x509write_crt_set_issuer_name(mbedtls_x509write_cert *ctx,
+                                          const char *issuer_name)
+{
+    return mbedtls_x509_string_to_names(&ctx->issuer, issuer_name);
+}
+
+#if defined(MBEDTLS_BIGNUM_C) && !defined(MBEDTLS_DEPRECATED_REMOVED)
+int mbedtls_x509write_crt_set_serial(mbedtls_x509write_cert *ctx,
+                                     const mbedtls_mpi *serial)
+{
+    int ret;
+    size_t tmp_len;
+
+    /* Ensure that the MPI value fits into the buffer */
+    tmp_len = mbedtls_mpi_size(serial);
+    if (tmp_len > MBEDTLS_X509_RFC5280_MAX_SERIAL_LEN) {
+        return MBEDTLS_ERR_X509_BAD_INPUT_DATA;
+    }
+
+    ctx->serial_len = tmp_len;
+
+    ret = mbedtls_mpi_write_binary(serial, ctx->serial, tmp_len);
+    if (ret < 0) {
+        return ret;
+    }
+
+    return 0;
+}
+#endif // MBEDTLS_BIGNUM_C && !MBEDTLS_DEPRECATED_REMOVED
+
+int mbedtls_x509write_crt_set_serial_raw(mbedtls_x509write_cert *ctx,
+                                         unsigned char *serial, size_t serial_len)
+{
+    if (serial_len > MBEDTLS_X509_RFC5280_MAX_SERIAL_LEN) {
+        return MBEDTLS_ERR_X509_BAD_INPUT_DATA;
+    }
+
+    ctx->serial_len = serial_len;
+    memcpy(ctx->serial, serial, serial_len);
+
+    return 0;
+}
+
+int mbedtls_x509write_crt_set_validity(mbedtls_x509write_cert *ctx,
+                                       const char *not_before,
+                                       const char *not_after)
+{
+    if (strlen(not_before) != MBEDTLS_X509_RFC5280_UTC_TIME_LEN - 1 ||
+        strlen(not_after)  != MBEDTLS_X509_RFC5280_UTC_TIME_LEN - 1) {
+        return MBEDTLS_ERR_X509_BAD_INPUT_DATA;
+    }
+    strncpy(ctx->not_before, not_before, MBEDTLS_X509_RFC5280_UTC_TIME_LEN);
+    strncpy(ctx->not_after, not_after, MBEDTLS_X509_RFC5280_UTC_TIME_LEN);
+    ctx->not_before[MBEDTLS_X509_RFC5280_UTC_TIME_LEN - 1] = 'Z';
+    ctx->not_after[MBEDTLS_X509_RFC5280_UTC_TIME_LEN - 1] = 'Z';
+
+    return 0;
+}
+
+int mbedtls_x509write_crt_set_subject_alternative_name(mbedtls_x509write_cert *ctx,
+                                                       const mbedtls_x509_san_list *san_list)
+{
+    return mbedtls_x509_write_set_san_common(&ctx->extensions, san_list);
+}
+
+
+int mbedtls_x509write_crt_set_extension(mbedtls_x509write_cert *ctx,
+                                        const char *oid, size_t oid_len,
+                                        int critical,
+                                        const unsigned char *val, size_t val_len)
+{
+    return mbedtls_x509_set_extension(&ctx->extensions, oid, oid_len,
+                                      critical, val, val_len);
+}
+
+int mbedtls_x509write_crt_set_basic_constraints(mbedtls_x509write_cert *ctx,
+                                                int is_ca, int max_pathlen)
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    unsigned char buf[9];
+    unsigned char *c = buf + sizeof(buf);
+    size_t len = 0;
+
+    memset(buf, 0, sizeof(buf));
+
+    if (is_ca && max_pathlen > 127) {
+        return MBEDTLS_ERR_X509_BAD_INPUT_DATA;
+    }
+
+    if (is_ca) {
+        if (max_pathlen >= 0) {
+            MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_int(&c, buf,
+                                                             max_pathlen));
+        }
+        MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_bool(&c, buf, 1));
+    }
+
+    MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(&c, buf, len));
+    MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_tag(&c, buf,
+                                                     MBEDTLS_ASN1_CONSTRUCTED |
+                                                     MBEDTLS_ASN1_SEQUENCE));
+
+    return
+        mbedtls_x509write_crt_set_extension(ctx, MBEDTLS_OID_BASIC_CONSTRAINTS,
+                                            MBEDTLS_OID_SIZE(MBEDTLS_OID_BASIC_CONSTRAINTS),
+                                            is_ca, buf + sizeof(buf) - len, len);
+}
+
+#if defined(MBEDTLS_MD_CAN_SHA1)
+static int mbedtls_x509write_crt_set_key_identifier(mbedtls_x509write_cert *ctx,
+                                                    int is_ca,
+                                                    unsigned char tag)
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    unsigned char buf[MBEDTLS_MPI_MAX_SIZE * 2 + 20]; /* tag, length + 2xMPI */
+    unsigned char *c = buf + sizeof(buf);
+    size_t len = 0;
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
+    psa_status_t status = PSA_ERROR_CORRUPTION_DETECTED;
+    size_t hash_length;
+#endif /* MBEDTLS_USE_PSA_CRYPTO */
+
+    memset(buf, 0, sizeof(buf));
+    MBEDTLS_ASN1_CHK_ADD(len,
+                         mbedtls_pk_write_pubkey(&c,
+                                                 buf,
+                                                 is_ca ?
+                                                 ctx->issuer_key :
+                                                 ctx->subject_key));
+
+
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
+    status = psa_hash_compute(PSA_ALG_SHA_1,
+                              buf + sizeof(buf) - len,
+                              len,
+                              buf + sizeof(buf) - 20,
+                              20,
+                              &hash_length);
+    if (status != PSA_SUCCESS) {
+        return MBEDTLS_ERR_PLATFORM_HW_ACCEL_FAILED;
+    }
+#else
+    ret = mbedtls_md(mbedtls_md_info_from_type(MBEDTLS_MD_SHA1),
+                     buf + sizeof(buf) - len, len,
+                     buf + sizeof(buf) - 20);
+    if (ret != 0) {
+        return ret;
+    }
+#endif /* MBEDTLS_USE_PSA_CRYPTO */
+
+    c = buf + sizeof(buf) - 20;
+    len = 20;
+
+    MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(&c, buf, len));
+    MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_tag(&c, buf, tag));
+
+    if (is_ca) { // writes AuthorityKeyIdentifier sequence
+        MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(&c, buf, len));
+        MBEDTLS_ASN1_CHK_ADD(len,
+                             mbedtls_asn1_write_tag(&c,
+                                                    buf,
+                                                    MBEDTLS_ASN1_CONSTRUCTED |
+                                                    MBEDTLS_ASN1_SEQUENCE));
+    }
+
+    if (is_ca) {
+        return mbedtls_x509write_crt_set_extension(ctx,
+                                                   MBEDTLS_OID_AUTHORITY_KEY_IDENTIFIER,
+                                                   MBEDTLS_OID_SIZE(
+                                                       MBEDTLS_OID_AUTHORITY_KEY_IDENTIFIER),
+                                                   0, buf + sizeof(buf) - len, len);
+    } else {
+        return mbedtls_x509write_crt_set_extension(ctx,
+                                                   MBEDTLS_OID_SUBJECT_KEY_IDENTIFIER,
+                                                   MBEDTLS_OID_SIZE(
+                                                       MBEDTLS_OID_SUBJECT_KEY_IDENTIFIER),
+                                                   0, buf + sizeof(buf) - len, len);
+    }
+}
+
+int mbedtls_x509write_crt_set_subject_key_identifier(mbedtls_x509write_cert *ctx)
+{
+    return mbedtls_x509write_crt_set_key_identifier(ctx,
+                                                    0,
+                                                    MBEDTLS_ASN1_OCTET_STRING);
+}
+
+int mbedtls_x509write_crt_set_authority_key_identifier(mbedtls_x509write_cert *ctx)
+{
+    return mbedtls_x509write_crt_set_key_identifier(ctx,
+                                                    1,
+                                                    (MBEDTLS_ASN1_CONTEXT_SPECIFIC | 0));
+}
+#endif /* MBEDTLS_MD_CAN_SHA1 */
+
+int mbedtls_x509write_crt_set_key_usage(mbedtls_x509write_cert *ctx,
+                                        unsigned int key_usage)
+{
+    unsigned char buf[5] = { 0 }, ku[2] = { 0 };
+    unsigned char *c;
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    const unsigned int allowed_bits = MBEDTLS_X509_KU_DIGITAL_SIGNATURE |
+                                      MBEDTLS_X509_KU_NON_REPUDIATION   |
+                                      MBEDTLS_X509_KU_KEY_ENCIPHERMENT  |
+                                      MBEDTLS_X509_KU_DATA_ENCIPHERMENT |
+                                      MBEDTLS_X509_KU_KEY_AGREEMENT     |
+                                      MBEDTLS_X509_KU_KEY_CERT_SIGN     |
+                                      MBEDTLS_X509_KU_CRL_SIGN          |
+                                      MBEDTLS_X509_KU_ENCIPHER_ONLY     |
+                                      MBEDTLS_X509_KU_DECIPHER_ONLY;
+
+    /* Check that nothing other than the allowed flags is set */
+    if ((key_usage & ~allowed_bits) != 0) {
+        return MBEDTLS_ERR_X509_FEATURE_UNAVAILABLE;
+    }
+
+    c = buf + 5;
+    MBEDTLS_PUT_UINT16_LE(key_usage, ku, 0);
+    ret = mbedtls_asn1_write_named_bitstring(&c, buf, ku, 9);
+
+    if (ret < 0) {
+        return ret;
+    } else if (ret < 3 || ret > 5) {
+        return MBEDTLS_ERR_X509_INVALID_FORMAT;
+    }
+
+    ret = mbedtls_x509write_crt_set_extension(ctx, MBEDTLS_OID_KEY_USAGE,
+                                              MBEDTLS_OID_SIZE(MBEDTLS_OID_KEY_USAGE),
+                                              1, c, (size_t) ret);
+    if (ret != 0) {
+        return ret;
+    }
+
+    return 0;
+}
+
+int mbedtls_x509write_crt_set_ext_key_usage(mbedtls_x509write_cert *ctx,
+                                            const mbedtls_asn1_sequence *exts)
+{
+    unsigned char buf[256];
+    unsigned char *c = buf + sizeof(buf);
+    int ret;
+    size_t len = 0;
+    const mbedtls_asn1_sequence *last_ext = NULL;
+    const mbedtls_asn1_sequence *ext;
+
+    memset(buf, 0, sizeof(buf));
+
+    /* We need at least one extension: SEQUENCE SIZE (1..MAX) OF KeyPurposeId */
+    if (exts == NULL) {
+        return MBEDTLS_ERR_X509_BAD_INPUT_DATA;
+    }
+
+    /* Iterate over exts backwards, so we write them out in the requested order */
+    while (last_ext != exts) {
+        for (ext = exts; ext->next != last_ext; ext = ext->next) {
+        }
+        if (ext->buf.tag != MBEDTLS_ASN1_OID) {
+            return MBEDTLS_ERR_X509_BAD_INPUT_DATA;
+        }
+        MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_raw_buffer(&c, buf, ext->buf.p, ext->buf.len));
+        MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(&c, buf, ext->buf.len));
+        MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_tag(&c, buf, MBEDTLS_ASN1_OID));
+        last_ext = ext;
+    }
+
+    MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(&c, buf, len));
+    MBEDTLS_ASN1_CHK_ADD(len,
+                         mbedtls_asn1_write_tag(&c, buf,
+                                                MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE));
+
+    return mbedtls_x509write_crt_set_extension(ctx,
+                                               MBEDTLS_OID_EXTENDED_KEY_USAGE,
+                                               MBEDTLS_OID_SIZE(MBEDTLS_OID_EXTENDED_KEY_USAGE),
+                                               1, c, len);
+}
+
+int mbedtls_x509write_crt_set_ns_cert_type(mbedtls_x509write_cert *ctx,
+                                           unsigned char ns_cert_type)
+{
+    unsigned char buf[4] = { 0 };
+    unsigned char *c;
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+
+    c = buf + 4;
+
+    ret = mbedtls_asn1_write_named_bitstring(&c, buf, &ns_cert_type, 8);
+    if (ret < 3 || ret > 4) {
+        return ret;
+    }
+
+    ret = mbedtls_x509write_crt_set_extension(ctx, MBEDTLS_OID_NS_CERT_TYPE,
+                                              MBEDTLS_OID_SIZE(MBEDTLS_OID_NS_CERT_TYPE),
+                                              0, c, (size_t) ret);
+    if (ret != 0) {
+        return ret;
+    }
+
+    return 0;
+}
+
+static int x509_write_time(unsigned char **p, unsigned char *start,
+                           const char *t, size_t size)
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    size_t len = 0;
+
+    /*
+     * write MBEDTLS_ASN1_UTC_TIME if year < 2050 (2 bytes shorter)
+     */
+    if (t[0] < '2' || (t[0] == '2' && t[1] == '0' && t[2] < '5')) {
+        MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_raw_buffer(p, start,
+                                                                (const unsigned char *) t + 2,
+                                                                size - 2));
+        MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(p, start, len));
+        MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_tag(p, start,
+                                                         MBEDTLS_ASN1_UTC_TIME));
+    } else {
+        MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_raw_buffer(p, start,
+                                                                (const unsigned char *) t,
+                                                                size));
+        MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(p, start, len));
+        MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_tag(p, start,
+                                                         MBEDTLS_ASN1_GENERALIZED_TIME));
+    }
+
+    return (int) len;
+}
+
+int mbedtls_x509write_crt_der(mbedtls_x509write_cert *ctx,
+                              unsigned char *buf, size_t size,
+                              int (*f_rng)(void *, unsigned char *, size_t),
+                              void *p_rng)
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    const char *sig_oid;
+    size_t sig_oid_len = 0;
+    unsigned char *c, *c2;
+    unsigned char sig[MBEDTLS_PK_SIGNATURE_MAX_SIZE];
+    size_t hash_length = 0;
+    unsigned char hash[MBEDTLS_MD_MAX_SIZE];
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
+    psa_status_t status = PSA_ERROR_CORRUPTION_DETECTED;
+    psa_algorithm_t psa_algorithm;
+#endif /* MBEDTLS_USE_PSA_CRYPTO */
+
+    size_t sub_len = 0, pub_len = 0, sig_and_oid_len = 0, sig_len;
+    size_t len = 0;
+    mbedtls_pk_type_t pk_alg;
+    int write_sig_null_par;
+
+    /*
+     * Prepare data to be signed at the end of the target buffer
+     */
+    c = buf + size;
+
+    /* Signature algorithm needed in TBS, and later for actual signature */
+
+    /* There's no direct way of extracting a signature algorithm
+     * (represented as an element of mbedtls_pk_type_t) from a PK instance. */
+    if (mbedtls_pk_can_do(ctx->issuer_key, MBEDTLS_PK_RSA)) {
+        pk_alg = MBEDTLS_PK_RSA;
+    } else if (mbedtls_pk_can_do(ctx->issuer_key, MBEDTLS_PK_ECDSA)) {
+        pk_alg = MBEDTLS_PK_ECDSA;
+    } else {
+        return MBEDTLS_ERR_X509_INVALID_ALG;
+    }
+
+    if ((ret = mbedtls_oid_get_oid_by_sig_alg(pk_alg, ctx->md_alg,
+                                              &sig_oid, &sig_oid_len)) != 0) {
+        return ret;
+    }
+
+    /*
+     *  Extensions  ::=  SEQUENCE SIZE (1..MAX) OF Extension
+     */
+
+    /* Only for v3 */
+    if (ctx->version == MBEDTLS_X509_CRT_VERSION_3) {
+        MBEDTLS_ASN1_CHK_ADD(len,
+                             mbedtls_x509_write_extensions(&c,
+                                                           buf, ctx->extensions));
+        MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(&c, buf, len));
+        MBEDTLS_ASN1_CHK_ADD(len,
+                             mbedtls_asn1_write_tag(&c, buf,
+                                                    MBEDTLS_ASN1_CONSTRUCTED |
+                                                    MBEDTLS_ASN1_SEQUENCE));
+        MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(&c, buf, len));
+        MBEDTLS_ASN1_CHK_ADD(len,
+                             mbedtls_asn1_write_tag(&c, buf,
+                                                    MBEDTLS_ASN1_CONTEXT_SPECIFIC |
+                                                    MBEDTLS_ASN1_CONSTRUCTED | 3));
+    }
+
+    /*
+     *  SubjectPublicKeyInfo
+     */
+    MBEDTLS_ASN1_CHK_ADD(pub_len,
+                         mbedtls_pk_write_pubkey_der(ctx->subject_key,
+                                                     buf, (size_t) (c - buf)));
+    c -= pub_len;
+    len += pub_len;
+
+    /*
+     *  Subject  ::=  Name
+     */
+    MBEDTLS_ASN1_CHK_ADD(len,
+                         mbedtls_x509_write_names(&c, buf,
+                                                  ctx->subject));
+
+    /*
+     *  Validity ::= SEQUENCE {
+     *       notBefore      Time,
+     *       notAfter       Time }
+     */
+    sub_len = 0;
+
+    MBEDTLS_ASN1_CHK_ADD(sub_len,
+                         x509_write_time(&c, buf, ctx->not_after,
+                                         MBEDTLS_X509_RFC5280_UTC_TIME_LEN));
+
+    MBEDTLS_ASN1_CHK_ADD(sub_len,
+                         x509_write_time(&c, buf, ctx->not_before,
+                                         MBEDTLS_X509_RFC5280_UTC_TIME_LEN));
+
+    len += sub_len;
+    MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(&c, buf, sub_len));
+    MBEDTLS_ASN1_CHK_ADD(len,
+                         mbedtls_asn1_write_tag(&c, buf,
+                                                MBEDTLS_ASN1_CONSTRUCTED |
+                                                MBEDTLS_ASN1_SEQUENCE));
+
+    /*
+     *  Issuer  ::=  Name
+     */
+    MBEDTLS_ASN1_CHK_ADD(len, mbedtls_x509_write_names(&c, buf,
+                                                       ctx->issuer));
+
+    /*
+     *  Signature   ::=  AlgorithmIdentifier
+     */
+    if (pk_alg == MBEDTLS_PK_ECDSA) {
+        /*
+         * The AlgorithmIdentifier's parameters field must be absent for DSA/ECDSA signature
+         * algorithms, see https://www.rfc-editor.org/rfc/rfc5480#page-17 and
+         * https://www.rfc-editor.org/rfc/rfc5758#section-3.
+         */
+        write_sig_null_par = 0;
+    } else {
+        write_sig_null_par = 1;
+    }
+    MBEDTLS_ASN1_CHK_ADD(len,
+                         mbedtls_asn1_write_algorithm_identifier_ext(&c, buf,
+                                                                     sig_oid, strlen(sig_oid),
+                                                                     0, write_sig_null_par));
+
+    /*
+     *  Serial   ::=  INTEGER
+     *
+     * Written data is:
+     * - "ctx->serial_len" bytes for the raw serial buffer
+     *   - if MSb of "serial" is 1, then prepend an extra 0x00 byte
+     * - 1 byte for the length
+     * - 1 byte for the TAG
+     */
+    MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_raw_buffer(&c, buf,
+                                                            ctx->serial, ctx->serial_len));
+    if (*c & 0x80) {
+        if (c - buf < 1) {
+            return MBEDTLS_ERR_X509_BUFFER_TOO_SMALL;
+        }
+        *(--c) = 0x0;
+        len++;
+        MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(&c, buf,
+                                                         ctx->serial_len + 1));
+    } else {
+        MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(&c, buf,
+                                                         ctx->serial_len));
+    }
+    MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_tag(&c, buf,
+                                                     MBEDTLS_ASN1_INTEGER));
+
+    /*
+     *  Version  ::=  INTEGER  {  v1(0), v2(1), v3(2)  }
+     */
+
+    /* Can be omitted for v1 */
+    if (ctx->version != MBEDTLS_X509_CRT_VERSION_1) {
+        sub_len = 0;
+        MBEDTLS_ASN1_CHK_ADD(sub_len,
+                             mbedtls_asn1_write_int(&c, buf, ctx->version));
+        len += sub_len;
+        MBEDTLS_ASN1_CHK_ADD(len,
+                             mbedtls_asn1_write_len(&c, buf, sub_len));
+        MBEDTLS_ASN1_CHK_ADD(len,
+                             mbedtls_asn1_write_tag(&c, buf,
+                                                    MBEDTLS_ASN1_CONTEXT_SPECIFIC |
+                                                    MBEDTLS_ASN1_CONSTRUCTED | 0));
+    }
+
+    MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(&c, buf, len));
+    MBEDTLS_ASN1_CHK_ADD(len,
+                         mbedtls_asn1_write_tag(&c, buf, MBEDTLS_ASN1_CONSTRUCTED |
+                                                MBEDTLS_ASN1_SEQUENCE));
+
+    /*
+     * Make signature
+     */
+
+    /* Compute hash of CRT. */
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
+    psa_algorithm = mbedtls_md_psa_alg_from_type(ctx->md_alg);
+
+    status = psa_hash_compute(psa_algorithm,
+                              c,
+                              len,
+                              hash,
+                              sizeof(hash),
+                              &hash_length);
+    if (status != PSA_SUCCESS) {
+        return MBEDTLS_ERR_PLATFORM_HW_ACCEL_FAILED;
+    }
+#else
+    if ((ret = mbedtls_md(mbedtls_md_info_from_type(ctx->md_alg), c,
+                          len, hash)) != 0) {
+        return ret;
+    }
+#endif /* MBEDTLS_USE_PSA_CRYPTO */
+
+
+    if ((ret = mbedtls_pk_sign(ctx->issuer_key, ctx->md_alg,
+                               hash, hash_length, sig, sizeof(sig), &sig_len,
+                               f_rng, p_rng)) != 0) {
+        return ret;
+    }
+
+    /* Move CRT to the front of the buffer to have space
+     * for the signature. */
+    memmove(buf, c, len);
+    c = buf + len;
+
+    /* Add signature at the end of the buffer,
+     * making sure that it doesn't underflow
+     * into the CRT buffer. */
+    c2 = buf + size;
+    MBEDTLS_ASN1_CHK_ADD(sig_and_oid_len, mbedtls_x509_write_sig(&c2, c,
+                                                                 sig_oid, sig_oid_len,
+                                                                 sig, sig_len, pk_alg));
+
+    /*
+     * Memory layout after this step:
+     *
+     * buf       c=buf+len                c2            buf+size
+     * [CRT0,...,CRTn, UNUSED, ..., UNUSED, SIG0, ..., SIGm]
+     */
+
+    /* Move raw CRT to just before the signature. */
+    c = c2 - len;
+    memmove(c, buf, len);
+
+    len += sig_and_oid_len;
+    MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(&c, buf, len));
+    MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_tag(&c, buf,
+                                                     MBEDTLS_ASN1_CONSTRUCTED |
+                                                     MBEDTLS_ASN1_SEQUENCE));
+
+    return (int) len;
+}
+
+#define PEM_BEGIN_CRT           "-----BEGIN CERTIFICATE-----\n"
+#define PEM_END_CRT             "-----END CERTIFICATE-----\n"
+
+#if defined(MBEDTLS_PEM_WRITE_C)
+int mbedtls_x509write_crt_pem(mbedtls_x509write_cert *crt,
+                              unsigned char *buf, size_t size,
+                              int (*f_rng)(void *, unsigned char *, size_t),
+                              void *p_rng)
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    size_t olen;
+
+    if ((ret = mbedtls_x509write_crt_der(crt, buf, size,
+                                         f_rng, p_rng)) < 0) {
+        return ret;
+    }
+
+    if ((ret = mbedtls_pem_write_buffer(PEM_BEGIN_CRT, PEM_END_CRT,
+                                        buf + size - ret, ret,
+                                        buf, size, &olen)) != 0) {
+        return ret;
+    }
+
+    return 0;
+}
+#endif /* MBEDTLS_PEM_WRITE_C */
+
+#endif /* MBEDTLS_X509_CRT_WRITE_C */