/*
 *  X.509 common functions for parsing and verification
 *
 *  Copyright The Mbed TLS Contributors
 *  SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
 */
/*
 *  The ITU-T X.509 standard defines a certificate format for PKI.
 *
 *  http://www.ietf.org/rfc/rfc5280.txt (Certificates and CRLs)
 *  http://www.ietf.org/rfc/rfc3279.txt (Alg IDs for CRLs)
 *  http://www.ietf.org/rfc/rfc2986.txt (CSRs, aka PKCS#10)
 *
 *  http://www.itu.int/ITU-T/studygroups/com17/languages/X.680-0207.pdf
 *  http://www.itu.int/ITU-T/studygroups/com17/languages/X.690-0207.pdf
 */

#include "common.h"

#if defined(MBEDTLS_X509_USE_C)

#include "mbedtls/x509.h"
#include "mbedtls/asn1.h"
#include "mbedtls/error.h"
#include "mbedtls/oid.h"

#include <stdio.h>
#include <string.h>

#if defined(MBEDTLS_PEM_PARSE_C)
#include "mbedtls/pem.h"
#endif

#include "mbedtls/platform.h"

#if defined(MBEDTLS_HAVE_TIME)
#include "mbedtls/platform_time.h"
#endif
#if defined(MBEDTLS_HAVE_TIME_DATE)
#include "mbedtls/platform_util.h"
#include <time.h>
#endif

#define CHECK(code)                                     \
    do {                                                \
        if ((ret = (code)) != 0) {                      \
            return ret;                                 \
        }                                               \
    } while (0)

#define CHECK_RANGE(min, max, val)                      \
    do {                                                \
        if ((val) < (min) || (val) > (max)) {           \
            return ret;                                 \
        }                                               \
    } while (0)

/*
 *  CertificateSerialNumber  ::=  INTEGER
 */
int mbedtls_x509_get_serial(unsigned char **p, const unsigned char *end,
                            mbedtls_x509_buf *serial)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

    if ((end - *p) < 1) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_SERIAL,
                                 MBEDTLS_ERR_ASN1_OUT_OF_DATA);
    }

    if (**p != (MBEDTLS_ASN1_CONTEXT_SPECIFIC | MBEDTLS_ASN1_PRIMITIVE | 2) &&
        **p !=   MBEDTLS_ASN1_INTEGER) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_SERIAL,
                                 MBEDTLS_ERR_ASN1_UNEXPECTED_TAG);
    }

    serial->tag = *(*p)++;

    if ((ret = mbedtls_asn1_get_len(p, end, &serial->len)) != 0) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_SERIAL, ret);
    }

    serial->p = *p;
    *p += serial->len;

    return 0;
}

/* Get an algorithm identifier without parameters (eg for signatures)
 *
 *  AlgorithmIdentifier  ::=  SEQUENCE  {
 *       algorithm               OBJECT IDENTIFIER,
 *       parameters              ANY DEFINED BY algorithm OPTIONAL  }
 */
int mbedtls_x509_get_alg_null(unsigned char **p, const unsigned char *end,
                              mbedtls_x509_buf *alg)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

    if ((ret = mbedtls_asn1_get_alg_null(p, end, alg)) != 0) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_ALG, ret);
    }

    return 0;
}

/*
 * Parse an algorithm identifier with (optional) parameters
 */
int mbedtls_x509_get_alg(unsigned char **p, const unsigned char *end,
                         mbedtls_x509_buf *alg, mbedtls_x509_buf *params)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

    if ((ret = mbedtls_asn1_get_alg(p, end, alg, params)) != 0) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_ALG, ret);
    }

    return 0;
}

#if defined(MBEDTLS_X509_RSASSA_PSS_SUPPORT)
/*
 * HashAlgorithm ::= AlgorithmIdentifier
 *
 * AlgorithmIdentifier  ::=  SEQUENCE  {
 *      algorithm               OBJECT IDENTIFIER,
 *      parameters              ANY DEFINED BY algorithm OPTIONAL  }
 *
 * For HashAlgorithm, parameters MUST be NULL or absent.
 */
static int x509_get_hash_alg(const mbedtls_x509_buf *alg, mbedtls_md_type_t *md_alg)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    unsigned char *p;
    const unsigned char *end;
    mbedtls_x509_buf md_oid;
    size_t len;

    /* Make sure we got a SEQUENCE and setup bounds */
    if (alg->tag != (MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE)) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_ALG,
                                 MBEDTLS_ERR_ASN1_UNEXPECTED_TAG);
    }

    p = alg->p;
    end = p + alg->len;

    if (p >= end) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_ALG,
                                 MBEDTLS_ERR_ASN1_OUT_OF_DATA);
    }

    /* Parse md_oid */
    md_oid.tag = *p;

    if ((ret = mbedtls_asn1_get_tag(&p, end, &md_oid.len, MBEDTLS_ASN1_OID)) != 0) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_ALG, ret);
    }

    md_oid.p = p;
    p += md_oid.len;

    /* Get md_alg from md_oid */
    if ((ret = mbedtls_oid_get_md_alg(&md_oid, md_alg)) != 0) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_ALG, ret);
    }

    /* Make sure params is absent of NULL */
    if (p == end) {
        return 0;
    }

    if ((ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_NULL)) != 0 || len != 0) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_ALG, ret);
    }

    if (p != end) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_ALG,
                                 MBEDTLS_ERR_ASN1_LENGTH_MISMATCH);
    }

    return 0;
}

/*
 *    RSASSA-PSS-params  ::=  SEQUENCE  {
 *       hashAlgorithm     [0] HashAlgorithm DEFAULT sha1Identifier,
 *       maskGenAlgorithm  [1] MaskGenAlgorithm DEFAULT mgf1SHA1Identifier,
 *       saltLength        [2] INTEGER DEFAULT 20,
 *       trailerField      [3] INTEGER DEFAULT 1  }
 *    -- Note that the tags in this Sequence are explicit.
 *
 * RFC 4055 (which defines use of RSASSA-PSS in PKIX) states that the value
 * of trailerField MUST be 1, and PKCS#1 v2.2 doesn't even define any other
 * option. Enforce this at parsing time.
 */
int mbedtls_x509_get_rsassa_pss_params(const mbedtls_x509_buf *params,
                                       mbedtls_md_type_t *md_alg, mbedtls_md_type_t *mgf_md,
                                       int *salt_len)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    unsigned char *p;
    const unsigned char *end, *end2;
    size_t len;
    mbedtls_x509_buf alg_id, alg_params;

    /* First set everything to defaults */
    *md_alg = MBEDTLS_MD_SHA1;
    *mgf_md = MBEDTLS_MD_SHA1;
    *salt_len = 20;

    /* Make sure params is a SEQUENCE and setup bounds */
    if (params->tag != (MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE)) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_ALG,
                                 MBEDTLS_ERR_ASN1_UNEXPECTED_TAG);
    }

    p = (unsigned char *) params->p;
    end = p + params->len;

    if (p == end) {
        return 0;
    }

    /*
     * HashAlgorithm
     */
    if ((ret = mbedtls_asn1_get_tag(&p, end, &len,
                                    MBEDTLS_ASN1_CONTEXT_SPECIFIC | MBEDTLS_ASN1_CONSTRUCTED |
                                    0)) == 0) {
        end2 = p + len;

        /* HashAlgorithm ::= AlgorithmIdentifier (without parameters) */
        if ((ret = mbedtls_x509_get_alg_null(&p, end2, &alg_id)) != 0) {
            return ret;
        }

        if ((ret = mbedtls_oid_get_md_alg(&alg_id, md_alg)) != 0) {
            return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_ALG, ret);
        }

        if (p != end2) {
            return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_ALG,
                                     MBEDTLS_ERR_ASN1_LENGTH_MISMATCH);
        }
    } else if (ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_ALG, ret);
    }

    if (p == end) {
        return 0;
    }

    /*
     * MaskGenAlgorithm
     */
    if ((ret = mbedtls_asn1_get_tag(&p, end, &len,
                                    MBEDTLS_ASN1_CONTEXT_SPECIFIC | MBEDTLS_ASN1_CONSTRUCTED |
                                    1)) == 0) {
        end2 = p + len;

        /* MaskGenAlgorithm ::= AlgorithmIdentifier (params = HashAlgorithm) */
        if ((ret = mbedtls_x509_get_alg(&p, end2, &alg_id, &alg_params)) != 0) {
            return ret;
        }

        /* Only MFG1 is recognised for now */
        if (MBEDTLS_OID_CMP(MBEDTLS_OID_MGF1, &alg_id) != 0) {
            return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_FEATURE_UNAVAILABLE,
                                     MBEDTLS_ERR_OID_NOT_FOUND);
        }

        /* Parse HashAlgorithm */
        if ((ret = x509_get_hash_alg(&alg_params, mgf_md)) != 0) {
            return ret;
        }

        if (p != end2) {
            return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_ALG,
                                     MBEDTLS_ERR_ASN1_LENGTH_MISMATCH);
        }
    } else if (ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_ALG, ret);
    }

    if (p == end) {
        return 0;
    }

    /*
     * salt_len
     */
    if ((ret = mbedtls_asn1_get_tag(&p, end, &len,
                                    MBEDTLS_ASN1_CONTEXT_SPECIFIC | MBEDTLS_ASN1_CONSTRUCTED |
                                    2)) == 0) {
        end2 = p + len;

        if ((ret = mbedtls_asn1_get_int(&p, end2, salt_len)) != 0) {
            return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_ALG, ret);
        }

        if (p != end2) {
            return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_ALG,
                                     MBEDTLS_ERR_ASN1_LENGTH_MISMATCH);
        }
    } else if (ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_ALG, ret);
    }

    if (p == end) {
        return 0;
    }

    /*
     * trailer_field (if present, must be 1)
     */
    if ((ret = mbedtls_asn1_get_tag(&p, end, &len,
                                    MBEDTLS_ASN1_CONTEXT_SPECIFIC | MBEDTLS_ASN1_CONSTRUCTED |
                                    3)) == 0) {
        int trailer_field;

        end2 = p + len;

        if ((ret = mbedtls_asn1_get_int(&p, end2, &trailer_field)) != 0) {
            return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_ALG, ret);
        }

        if (p != end2) {
            return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_ALG,
                                     MBEDTLS_ERR_ASN1_LENGTH_MISMATCH);
        }

        if (trailer_field != 1) {
            return MBEDTLS_ERR_X509_INVALID_ALG;
        }
    } else if (ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_ALG, ret);
    }

    if (p != end) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_ALG,
                                 MBEDTLS_ERR_ASN1_LENGTH_MISMATCH);
    }

    return 0;
}
#endif /* MBEDTLS_X509_RSASSA_PSS_SUPPORT */

/*
 *  AttributeTypeAndValue ::= SEQUENCE {
 *    type     AttributeType,
 *    value    AttributeValue }
 *
 *  AttributeType ::= OBJECT IDENTIFIER
 *
 *  AttributeValue ::= ANY DEFINED BY AttributeType
 */
static int x509_get_attr_type_value(unsigned char **p,
                                    const unsigned char *end,
                                    mbedtls_x509_name *cur)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    size_t len;
    mbedtls_x509_buf *oid;
    mbedtls_x509_buf *val;

    if ((ret = mbedtls_asn1_get_tag(p, end, &len,
                                    MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE)) != 0) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_NAME, ret);
    }

    end = *p + len;

    if ((end - *p) < 1) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_NAME,
                                 MBEDTLS_ERR_ASN1_OUT_OF_DATA);
    }

    oid = &cur->oid;
    oid->tag = **p;

    if ((ret = mbedtls_asn1_get_tag(p, end, &oid->len, MBEDTLS_ASN1_OID)) != 0) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_NAME, ret);
    }

    oid->p = *p;
    *p += oid->len;

    if ((end - *p) < 1) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_NAME,
                                 MBEDTLS_ERR_ASN1_OUT_OF_DATA);
    }

    if (**p != MBEDTLS_ASN1_BMP_STRING && **p != MBEDTLS_ASN1_UTF8_STRING      &&
        **p != MBEDTLS_ASN1_T61_STRING && **p != MBEDTLS_ASN1_PRINTABLE_STRING &&
        **p != MBEDTLS_ASN1_IA5_STRING && **p != MBEDTLS_ASN1_UNIVERSAL_STRING &&
        **p != MBEDTLS_ASN1_BIT_STRING) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_NAME,
                                 MBEDTLS_ERR_ASN1_UNEXPECTED_TAG);
    }

    val = &cur->val;
    val->tag = *(*p)++;

    if ((ret = mbedtls_asn1_get_len(p, end, &val->len)) != 0) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_NAME, ret);
    }

    val->p = *p;
    *p += val->len;

    if (*p != end) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_NAME,
                                 MBEDTLS_ERR_ASN1_LENGTH_MISMATCH);
    }

    cur->next = NULL;

    return 0;
}

/*
 *  Name ::= CHOICE { -- only one possibility for now --
 *       rdnSequence  RDNSequence }
 *
 *  RDNSequence ::= SEQUENCE OF RelativeDistinguishedName
 *
 *  RelativeDistinguishedName ::=
 *    SET OF AttributeTypeAndValue
 *
 *  AttributeTypeAndValue ::= SEQUENCE {
 *    type     AttributeType,
 *    value    AttributeValue }
 *
 *  AttributeType ::= OBJECT IDENTIFIER
 *
 *  AttributeValue ::= ANY DEFINED BY AttributeType
 *
 * The data structure is optimized for the common case where each RDN has only
 * one element, which is represented as a list of AttributeTypeAndValue.
 * For the general case we still use a flat list, but we mark elements of the
 * same set so that they are "merged" together in the functions that consume
 * this list, eg mbedtls_x509_dn_gets().
 *
 * On success, this function may allocate a linked list starting at cur->next
 * that must later be free'd by the caller using mbedtls_free(). In error
 * cases, this function frees all allocated memory internally and the caller
 * has no freeing responsibilities.
 */
int mbedtls_x509_get_name(unsigned char **p, const unsigned char *end,
                          mbedtls_x509_name *cur)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    size_t set_len;
    const unsigned char *end_set;
    mbedtls_x509_name *head = cur;
    mbedtls_x509_name *prev, *allocated;

    /* don't use recursion, we'd risk stack overflow if not optimized */
    while (1) {
        /*
         * parse SET
         */
        if ((ret = mbedtls_asn1_get_tag(p, end, &set_len,
                                        MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SET)) != 0) {
            ret = MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_NAME, ret);
            goto error;
        }

        end_set  = *p + set_len;

        while (1) {
            if ((ret = x509_get_attr_type_value(p, end_set, cur)) != 0) {
                goto error;
            }

            if (*p == end_set) {
                break;
            }

            /* Mark this item as being no the only one in a set */
            cur->next_merged = 1;

            cur->next = mbedtls_calloc(1, sizeof(mbedtls_x509_name));

            if (cur->next == NULL) {
                ret = MBEDTLS_ERR_X509_ALLOC_FAILED;
                goto error;
            }

            cur = cur->next;
        }

        /*
         * continue until end of SEQUENCE is reached
         */
        if (*p == end) {
            return 0;
        }

        cur->next = mbedtls_calloc(1, sizeof(mbedtls_x509_name));

        if (cur->next == NULL) {
            ret = MBEDTLS_ERR_X509_ALLOC_FAILED;
            goto error;
        }

        cur = cur->next;
    }

error:
    /* Skip the first element as we did not allocate it */
    allocated = head->next;

    while (allocated != NULL) {
        prev = allocated;
        allocated = allocated->next;

        mbedtls_platform_zeroize(prev, sizeof(*prev));
        mbedtls_free(prev);
    }

    mbedtls_platform_zeroize(head, sizeof(*head));

    return ret;
}

static int x509_parse_int(unsigned char **p, size_t n, int *res)
{
    *res = 0;

    for (; n > 0; --n) {
        if ((**p < '0') || (**p > '9')) {
            return MBEDTLS_ERR_X509_INVALID_DATE;
        }

        *res *= 10;
        *res += (*(*p)++ - '0');
    }

    return 0;
}

static int x509_date_is_valid(const mbedtls_x509_time *t)
{
    int ret = MBEDTLS_ERR_X509_INVALID_DATE;
    int month_len;

    CHECK_RANGE(0, 9999, t->year);
    CHECK_RANGE(0, 23,   t->hour);
    CHECK_RANGE(0, 59,   t->min);
    CHECK_RANGE(0, 59,   t->sec);

    switch (t->mon) {
        case 1: case 3: case 5: case 7: case 8: case 10: case 12:
            month_len = 31;
            break;
        case 4: case 6: case 9: case 11:
            month_len = 30;
            break;
        case 2:
            if ((!(t->year % 4) && t->year % 100) ||
                !(t->year % 400)) {
                month_len = 29;
            } else {
                month_len = 28;
            }
            break;
        default:
            return ret;
    }
    CHECK_RANGE(1, month_len, t->day);

    return 0;
}

/*
 * Parse an ASN1_UTC_TIME (yearlen=2) or ASN1_GENERALIZED_TIME (yearlen=4)
 * field.
 */
static int x509_parse_time(unsigned char **p, size_t len, size_t yearlen,
                           mbedtls_x509_time *tm)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

    /*
     * Minimum length is 10 or 12 depending on yearlen
     */
    if (len < yearlen + 8) {
        return MBEDTLS_ERR_X509_INVALID_DATE;
    }
    len -= yearlen + 8;

    /*
     * Parse year, month, day, hour, minute
     */
    CHECK(x509_parse_int(p, yearlen, &tm->year));
    if (2 == yearlen) {
        if (tm->year < 50) {
            tm->year += 100;
        }

        tm->year += 1900;
    }

    CHECK(x509_parse_int(p, 2, &tm->mon));
    CHECK(x509_parse_int(p, 2, &tm->day));
    CHECK(x509_parse_int(p, 2, &tm->hour));
    CHECK(x509_parse_int(p, 2, &tm->min));

    /*
     * Parse seconds if present
     */
    if (len >= 2) {
        CHECK(x509_parse_int(p, 2, &tm->sec));
        len -= 2;
    } else {
        return MBEDTLS_ERR_X509_INVALID_DATE;
    }

    /*
     * Parse trailing 'Z' if present
     */
    if (1 == len && 'Z' == **p) {
        (*p)++;
        len--;
    }

    /*
     * We should have parsed all characters at this point
     */
    if (0 != len) {
        return MBEDTLS_ERR_X509_INVALID_DATE;
    }

    CHECK(x509_date_is_valid(tm));

    return 0;
}

/*
 *  Time ::= CHOICE {
 *       utcTime        UTCTime,
 *       generalTime    GeneralizedTime }
 */
int mbedtls_x509_get_time(unsigned char **p, const unsigned char *end,
                          mbedtls_x509_time *tm)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    size_t len, year_len;
    unsigned char tag;

    if ((end - *p) < 1) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_DATE,
                                 MBEDTLS_ERR_ASN1_OUT_OF_DATA);
    }

    tag = **p;

    if (tag == MBEDTLS_ASN1_UTC_TIME) {
        year_len = 2;
    } else if (tag == MBEDTLS_ASN1_GENERALIZED_TIME) {
        year_len = 4;
    } else {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_DATE,
                                 MBEDTLS_ERR_ASN1_UNEXPECTED_TAG);
    }

    (*p)++;
    ret = mbedtls_asn1_get_len(p, end, &len);

    if (ret != 0) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_DATE, ret);
    }

    return x509_parse_time(p, len, year_len, tm);
}

int mbedtls_x509_get_sig(unsigned char **p, const unsigned char *end, mbedtls_x509_buf *sig)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    size_t len;
    int tag_type;

    if ((end - *p) < 1) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_SIGNATURE,
                                 MBEDTLS_ERR_ASN1_OUT_OF_DATA);
    }

    tag_type = **p;

    if ((ret = mbedtls_asn1_get_bitstring_null(p, end, &len)) != 0) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_SIGNATURE, ret);
    }

    sig->tag = tag_type;
    sig->len = len;
    sig->p = *p;

    *p += len;

    return 0;
}

/*
 * Get signature algorithm from alg OID and optional parameters
 */
int mbedtls_x509_get_sig_alg(const mbedtls_x509_buf *sig_oid, const mbedtls_x509_buf *sig_params,
                             mbedtls_md_type_t *md_alg, mbedtls_pk_type_t *pk_alg,
                             void **sig_opts)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

    if (*sig_opts != NULL) {
        return MBEDTLS_ERR_X509_BAD_INPUT_DATA;
    }

    if ((ret = mbedtls_oid_get_sig_alg(sig_oid, md_alg, pk_alg)) != 0) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_UNKNOWN_SIG_ALG, ret);
    }

#if defined(MBEDTLS_X509_RSASSA_PSS_SUPPORT)
    if (*pk_alg == MBEDTLS_PK_RSASSA_PSS) {
        mbedtls_pk_rsassa_pss_options *pss_opts;

        pss_opts = mbedtls_calloc(1, sizeof(mbedtls_pk_rsassa_pss_options));
        if (pss_opts == NULL) {
            return MBEDTLS_ERR_X509_ALLOC_FAILED;
        }

        ret = mbedtls_x509_get_rsassa_pss_params(sig_params,
                                                 md_alg,
                                                 &pss_opts->mgf1_hash_id,
                                                 &pss_opts->expected_salt_len);
        if (ret != 0) {
            mbedtls_free(pss_opts);
            return ret;
        }

        *sig_opts = (void *) pss_opts;
    } else
#endif /* MBEDTLS_X509_RSASSA_PSS_SUPPORT */
    {
        /* Make sure parameters are absent or NULL */
        if ((sig_params->tag != MBEDTLS_ASN1_NULL && sig_params->tag != 0) ||
            sig_params->len != 0) {
            return MBEDTLS_ERR_X509_INVALID_ALG;
        }
    }

    return 0;
}

/*
 * X.509 Extensions (No parsing of extensions, pointer should
 * be either manually updated or extensions should be parsed!)
 */
int mbedtls_x509_get_ext(unsigned char **p, const unsigned char *end,
                         mbedtls_x509_buf *ext, int tag)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    size_t len;

    /* Extension structure use EXPLICIT tagging. That is, the actual
     * `Extensions` structure is wrapped by a tag-length pair using
     * the respective context-specific tag. */
    ret = mbedtls_asn1_get_tag(p, end, &ext->len,
                               MBEDTLS_ASN1_CONTEXT_SPECIFIC | MBEDTLS_ASN1_CONSTRUCTED | tag);
    if (ret != 0) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS, ret);
    }

    ext->tag = MBEDTLS_ASN1_CONTEXT_SPECIFIC | MBEDTLS_ASN1_CONSTRUCTED | tag;
    ext->p   = *p;
    end      = *p + ext->len;

    /*
     * Extensions  ::=  SEQUENCE SIZE (1..MAX) OF Extension
     */
    if ((ret = mbedtls_asn1_get_tag(p, end, &len,
                                    MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE)) != 0) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS, ret);
    }

    if (end != *p + len) {
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS,
                                 MBEDTLS_ERR_ASN1_LENGTH_MISMATCH);
    }

    return 0;
}

/*
 * Store the name in printable form into buf; no more
 * than size characters will be written
 */
int mbedtls_x509_dn_gets(char *buf, size_t size, const mbedtls_x509_name *dn)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    size_t i, j, n;
    unsigned char c, merge = 0;
    const mbedtls_x509_name *name;
    const char *short_name = NULL;
    char s[MBEDTLS_X509_MAX_DN_NAME_SIZE], *p;

    memset(s, 0, sizeof(s));

    name = dn;
    p = buf;
    n = size;

    while (name != NULL) {
        if (!name->oid.p) {
            name = name->next;
            continue;
        }

        if (name != dn) {
            ret = mbedtls_snprintf(p, n, merge ? " + " : ", ");
            MBEDTLS_X509_SAFE_SNPRINTF;
        }

        ret = mbedtls_oid_get_attr_short_name(&name->oid, &short_name);

        if (ret == 0) {
            ret = mbedtls_snprintf(p, n, "%s=", short_name);
        } else {
            ret = mbedtls_snprintf(p, n, "\?\?=");
        }
        MBEDTLS_X509_SAFE_SNPRINTF;

        for (i = 0, j = 0; i < name->val.len; i++, j++) {
            if (j >= sizeof(s) - 1) {
                return MBEDTLS_ERR_X509_BUFFER_TOO_SMALL;
            }

            c = name->val.p[i];
            // Special characters requiring escaping, RFC 1779
            if (c && strchr(",=+<>#;\"\\", c)) {
                if (j + 1 >= sizeof(s) - 1) {
                    return MBEDTLS_ERR_X509_BUFFER_TOO_SMALL;
                }
                s[j++] = '\\';
            }
            if (c < 32 || c >= 127) {
                s[j] = '?';
            } else {
                s[j] = c;
            }
        }
        s[j] = '\0';
        ret = mbedtls_snprintf(p, n, "%s", s);
        MBEDTLS_X509_SAFE_SNPRINTF;

        merge = name->next_merged;
        name = name->next;
    }

    return (int) (size - n);
}

/*
 * Store the serial in printable form into buf; no more
 * than size characters will be written
 */
int mbedtls_x509_serial_gets(char *buf, size_t size, const mbedtls_x509_buf *serial)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    size_t i, n, nr;
    char *p;

    p = buf;
    n = size;

    nr = (serial->len <= 32)
        ? serial->len  : 28;

    for (i = 0; i < nr; i++) {
        if (i == 0 && nr > 1 && serial->p[i] == 0x0) {
            continue;
        }

        ret = mbedtls_snprintf(p, n, "%02X%s",
                               serial->p[i], (i < nr - 1) ? ":" : "");
        MBEDTLS_X509_SAFE_SNPRINTF;
    }

    if (nr != serial->len) {
        ret = mbedtls_snprintf(p, n, "....");
        MBEDTLS_X509_SAFE_SNPRINTF;
    }

    return (int) (size - n);
}

/*
 * Helper for writing signature algorithms
 */
int mbedtls_x509_sig_alg_gets(char *buf, size_t size, const mbedtls_x509_buf *sig_oid,
                              mbedtls_pk_type_t pk_alg, mbedtls_md_type_t md_alg,
                              const void *sig_opts)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    char *p = buf;
    size_t n = size;
    const char *desc = NULL;

    ret = mbedtls_oid_get_sig_alg_desc(sig_oid, &desc);
    if (ret != 0) {
        ret = mbedtls_snprintf(p, n, "???");
    } else {
        ret = mbedtls_snprintf(p, n, "%s", desc);
    }
    MBEDTLS_X509_SAFE_SNPRINTF;

#if defined(MBEDTLS_X509_RSASSA_PSS_SUPPORT)
    if (pk_alg == MBEDTLS_PK_RSASSA_PSS) {
        const mbedtls_pk_rsassa_pss_options *pss_opts;
        const mbedtls_md_info_t *md_info, *mgf_md_info;

        pss_opts = (const mbedtls_pk_rsassa_pss_options *) sig_opts;

        md_info = mbedtls_md_info_from_type(md_alg);
        mgf_md_info = mbedtls_md_info_from_type(pss_opts->mgf1_hash_id);

        ret = mbedtls_snprintf(p, n, " (%s, MGF1-%s, 0x%02X)",
                               md_info ? mbedtls_md_get_name(md_info) : "???",
                               mgf_md_info ? mbedtls_md_get_name(mgf_md_info) : "???",
                               (unsigned int) pss_opts->expected_salt_len);
        MBEDTLS_X509_SAFE_SNPRINTF;
    }
#else
    ((void) pk_alg);
    ((void) md_alg);
    ((void) sig_opts);
#endif /* MBEDTLS_X509_RSASSA_PSS_SUPPORT */

    return (int) (size - n);
}

/*
 * Helper for writing "RSA key size", "EC key size", etc
 */
int mbedtls_x509_key_size_helper(char *buf, size_t buf_size, const char *name)
{
    char *p = buf;
    size_t n = buf_size;
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

    ret = mbedtls_snprintf(p, n, "%s key size", name);
    MBEDTLS_X509_SAFE_SNPRINTF;

    return 0;
}

#if defined(MBEDTLS_HAVE_TIME_DATE)
/*
 * Set the time structure to the current time.
 * Return 0 on success, non-zero on failure.
 */
static int x509_get_current_time(mbedtls_x509_time *now)
{
    struct tm *lt, tm_buf;
    mbedtls_time_t tt;
    int ret = 0;

    tt = mbedtls_time(NULL);
    lt = mbedtls_platform_gmtime_r(&tt, &tm_buf);

    if (lt == NULL) {
        ret = -1;
    } else {
        now->year = lt->tm_year + 1900;
        now->mon  = lt->tm_mon  + 1;
        now->day  = lt->tm_mday;
        now->hour = lt->tm_hour;
        now->min  = lt->tm_min;
        now->sec  = lt->tm_sec;
    }

    return ret;
}

/*
 * Return 0 if before <= after, 1 otherwise
 */
static int x509_check_time(const mbedtls_x509_time *before, const mbedtls_x509_time *after)
{
    if (before->year  > after->year) {
        return 1;
    }

    if (before->year == after->year &&
        before->mon   > after->mon) {
        return 1;
    }

    if (before->year == after->year &&
        before->mon  == after->mon  &&
        before->day   > after->day) {
        return 1;
    }

    if (before->year == after->year &&
        before->mon  == after->mon  &&
        before->day  == after->day  &&
        before->hour  > after->hour) {
        return 1;
    }

    if (before->year == after->year &&
        before->mon  == after->mon  &&
        before->day  == after->day  &&
        before->hour == after->hour &&
        before->min   > after->min) {
        return 1;
    }

    if (before->year == after->year &&
        before->mon  == after->mon  &&
        before->day  == after->day  &&
        before->hour == after->hour &&
        before->min  == after->min  &&
        before->sec   > after->sec) {
        return 1;
    }

    return 0;
}

int mbedtls_x509_time_is_past(const mbedtls_x509_time *to)
{
    mbedtls_x509_time now;

    if (x509_get_current_time(&now) != 0) {
        return 1;
    }

    return x509_check_time(&now, to);
}

int mbedtls_x509_time_is_future(const mbedtls_x509_time *from)
{
    mbedtls_x509_time now;

    if (x509_get_current_time(&now) != 0) {
        return 1;
    }

    return x509_check_time(from, &now);
}

#else  /* MBEDTLS_HAVE_TIME_DATE */

int mbedtls_x509_time_is_past(const mbedtls_x509_time *to)
{
    ((void) to);
    return 0;
}

int mbedtls_x509_time_is_future(const mbedtls_x509_time *from)
{
    ((void) from);
    return 0;
}
#endif /* MBEDTLS_HAVE_TIME_DATE */

#if defined(MBEDTLS_SELF_TEST)

#include "mbedtls/x509_crt.h"
#include "mbedtls/certs.h"

/*
 * Checkup routine
 */
int mbedtls_x509_self_test(int verbose)
{
    int ret = 0;
#if defined(MBEDTLS_CERTS_C) && defined(MBEDTLS_SHA256_C)
    uint32_t flags;
    mbedtls_x509_crt cacert;
    mbedtls_x509_crt clicert;

    if (verbose != 0) {
        mbedtls_printf("  X.509 certificate load: ");
    }

    mbedtls_x509_crt_init(&cacert);
    mbedtls_x509_crt_init(&clicert);

    ret = mbedtls_x509_crt_parse(&clicert, (const unsigned char *) mbedtls_test_cli_crt,
                                 mbedtls_test_cli_crt_len);
    if (ret != 0) {
        if (verbose != 0) {
            mbedtls_printf("failed\n");
        }

        goto cleanup;
    }

    ret = mbedtls_x509_crt_parse(&cacert, (const unsigned char *) mbedtls_test_ca_crt,
                                 mbedtls_test_ca_crt_len);
    if (ret != 0) {
        if (verbose != 0) {
            mbedtls_printf("failed\n");
        }

        goto cleanup;
    }

    if (verbose != 0) {
        mbedtls_printf("passed\n  X.509 signature verify: ");
    }

    ret = mbedtls_x509_crt_verify(&clicert, &cacert, NULL, NULL, &flags, NULL, NULL);
    if (ret != 0) {
        if (verbose != 0) {
            mbedtls_printf("failed\n");
        }

        goto cleanup;
    }

    if (verbose != 0) {
        mbedtls_printf("passed\n\n");
    }

cleanup:
    mbedtls_x509_crt_free(&cacert);
    mbedtls_x509_crt_free(&clicert);
#else
    ((void) verbose);
#endif /* MBEDTLS_CERTS_C && MBEDTLS_SHA256_C */
    return ret;
}

#endif /* MBEDTLS_SELF_TEST */

#endif /* MBEDTLS_X509_USE_C */