openssl/crypto/ct/ct_sct_ctx.c

/*
 * Copyright 2016-2021 The OpenSSL Project Authors. All Rights Reserved.
 *
 * Licensed under the Apache License 2.0 (the "License").  You may not use
 * this file except in compliance with the License.  You can obtain a copy
 * in the file LICENSE in the source distribution or at
 * https://www.openssl.org/source/license.html
 */

#ifdef OPENSSL_NO_CT
# error "CT is disabled"
#endif

#include <stddef.h>
#include <string.h>

#include <openssl/err.h>
#include <openssl/obj_mac.h>
#include <openssl/x509.h>

#include "ct_local.h"

SCT_CTX *SCT_CTX_new(OSSL_LIB_CTX *libctx, const char *propq)
{
    SCT_CTX *sctx = OPENSSL_zalloc(sizeof(*sctx));

    if (sctx == NULL)
        return NULL;

    sctx->libctx = libctx;
    if (propq != NULL) {
        sctx->propq = OPENSSL_strdup(propq);
        if (sctx->propq == NULL) {
            OPENSSL_free(sctx);
            return NULL;
        }
    }

    return sctx;
}

void SCT_CTX_free(SCT_CTX *sctx)
{
    if (sctx == NULL)
        return;
    EVP_PKEY_free(sctx->pkey);
    OPENSSL_free(sctx->pkeyhash);
    OPENSSL_free(sctx->ihash);
    OPENSSL_free(sctx->certder);
    OPENSSL_free(sctx->preder);
    OPENSSL_free(sctx->propq);
    OPENSSL_free(sctx);
}

/*
 * Finds the index of the first extension with the given NID in cert.
 * If there is more than one extension with that NID, *is_duplicated is set to
 * 1, otherwise 0 (unless it is NULL).
 */
static int ct_x509_get_ext(X509 *cert, int nid, int *is_duplicated)
{
    int ret = X509_get_ext_by_NID(cert, nid, -1);

    if (is_duplicated != NULL)
        *is_duplicated = ret >= 0 && X509_get_ext_by_NID(cert, nid, ret) >= 0;

    return ret;
}

/*
 * Modifies a certificate by deleting extensions and copying the issuer and
 * AKID from the presigner certificate, if necessary.
 * Returns 1 on success, 0 otherwise.
 */
__owur static int ct_x509_cert_fixup(X509 *cert, X509 *presigner)
{
    int preidx, certidx;
    int pre_akid_ext_is_dup, cert_akid_ext_is_dup;

    if (presigner == NULL)
        return 1;

    preidx = ct_x509_get_ext(presigner, NID_authority_key_identifier,
                             &pre_akid_ext_is_dup);
    certidx = ct_x509_get_ext(cert, NID_authority_key_identifier,
                              &cert_akid_ext_is_dup);

    /* An error occurred whilst searching for the extension */
    if (preidx < -1 || certidx < -1)
        return 0;
    /* Invalid certificate if they contain duplicate extensions */
    if (pre_akid_ext_is_dup || cert_akid_ext_is_dup)
        return 0;
    /* AKID must be present in both certificate or absent in both */
    if (preidx >= 0 && certidx == -1)
        return 0;
    if (preidx == -1 && certidx >= 0)
        return 0;
    /* Copy issuer name */
    if (!X509_set_issuer_name(cert, X509_get_issuer_name(presigner)))
        return 0;
    if (preidx != -1) {
        /* Retrieve and copy AKID encoding */
        X509_EXTENSION *preext = X509_get_ext(presigner, preidx);
        X509_EXTENSION *certext = X509_get_ext(cert, certidx);
        ASN1_OCTET_STRING *preextdata;

        /* Should never happen */
        if (preext == NULL || certext == NULL)
            return 0;
        preextdata = X509_EXTENSION_get_data(preext);
        if (preextdata == NULL ||
            !X509_EXTENSION_set_data(certext, preextdata))
            return 0;
    }
    return 1;
}

int SCT_CTX_set1_cert(SCT_CTX *sctx, X509 *cert, X509 *presigner)
{
    unsigned char *certder = NULL, *preder = NULL;
    X509 *pretmp = NULL;
    int certderlen = 0, prederlen = 0;
    int idx = -1;
    int poison_ext_is_dup, sct_ext_is_dup;
    int poison_idx = ct_x509_get_ext(cert, NID_ct_precert_poison, &poison_ext_is_dup);

    /* Duplicate poison extensions are present - error */
    if (poison_ext_is_dup)
        goto err;

    /* If *cert doesn't have a poison extension, it isn't a precert */
    if (poison_idx == -1) {
        /* cert isn't a precert, so we shouldn't have a presigner */
        if (presigner != NULL)
            goto err;

        certderlen = i2d_X509(cert, &certder);
        if (certderlen < 0)
            goto err;
    }

    /* See if cert has a precert SCTs extension */
    idx = ct_x509_get_ext(cert, NID_ct_precert_scts, &sct_ext_is_dup);
    /* Duplicate SCT extensions are present - error */
    if (sct_ext_is_dup)
        goto err;

    if (idx >= 0 && poison_idx >= 0) {
        /*
         * cert can't both contain SCTs (i.e. have an SCT extension) and be a
         * precert (i.e. have a poison extension).
         */
        goto err;
    }

    if (idx == -1) {
        idx = poison_idx;
    }

    /*
     * If either a poison or SCT extension is present, remove it before encoding
     * cert. This, along with ct_x509_cert_fixup(), gets a TBSCertificate (see
     * RFC5280) from cert, which is what the CT log signed when it produced the
     * SCT.
     */
    if (idx >= 0) {
        /* Take a copy of certificate so we don't modify passed version */
        pretmp = X509_dup(cert);
        if (pretmp == NULL)
            goto err;

        X509_EXTENSION_free(X509_delete_ext(pretmp, idx));

        if (!ct_x509_cert_fixup(pretmp, presigner))
            goto err;

        prederlen = i2d_re_X509_tbs(pretmp, &preder);
        if (prederlen <= 0)
            goto err;
    }

    X509_free(pretmp);

    OPENSSL_free(sctx->certder);
    sctx->certder = certder;
    sctx->certderlen = certderlen;

    OPENSSL_free(sctx->preder);
    sctx->preder = preder;
    sctx->prederlen = prederlen;

    return 1;
err:
    OPENSSL_free(certder);
    OPENSSL_free(preder);
    X509_free(pretmp);
    return 0;
}

__owur static int ct_public_key_hash(SCT_CTX *sctx, X509_PUBKEY *pkey,
                                     unsigned char **hash, size_t *hash_len)
{
    int ret = 0;
    unsigned char *md = NULL, *der = NULL;
    int der_len;
    unsigned int md_len;
    EVP_MD *sha256 = EVP_MD_fetch(sctx->libctx, "SHA2-256", sctx->propq);

    if (sha256 == NULL)
        goto err;

    /* Reuse buffer if possible */
    if (*hash != NULL && *hash_len >= SHA256_DIGEST_LENGTH) {
        md = *hash;
    } else {
        md = OPENSSL_malloc(SHA256_DIGEST_LENGTH);
        if (md == NULL)
            goto err;
    }

    /* Calculate key hash */
    der_len = i2d_X509_PUBKEY(pkey, &der);
    if (der_len <= 0)
        goto err;

    if (!EVP_Digest(der, der_len, md, &md_len, sha256, NULL))
        goto err;

    if (md != *hash) {
        OPENSSL_free(*hash);
        *hash = md;
        *hash_len = SHA256_DIGEST_LENGTH;
    }

    md = NULL;
    ret = 1;
 err:
    EVP_MD_free(sha256);
    OPENSSL_free(md);
    OPENSSL_free(der);
    return ret;
}

int SCT_CTX_set1_issuer(SCT_CTX *sctx, const X509 *issuer)
{
    return SCT_CTX_set1_issuer_pubkey(sctx, X509_get_X509_PUBKEY(issuer));
}

int SCT_CTX_set1_issuer_pubkey(SCT_CTX *sctx, X509_PUBKEY *pubkey)
{
    return ct_public_key_hash(sctx, pubkey, &sctx->ihash, &sctx->ihashlen);
}

int SCT_CTX_set1_pubkey(SCT_CTX *sctx, X509_PUBKEY *pubkey)
{
    EVP_PKEY *pkey = X509_PUBKEY_get(pubkey);

    if (pkey == NULL)
        return 0;

    if (!ct_public_key_hash(sctx, pubkey, &sctx->pkeyhash, &sctx->pkeyhashlen)) {
        EVP_PKEY_free(pkey);
        return 0;
    }

    EVP_PKEY_free(sctx->pkey);
    sctx->pkey = pkey;
    return 1;
}

void SCT_CTX_set_time(SCT_CTX *sctx, uint64_t time_in_ms)
{
    sctx->epoch_time_in_ms = time_in_ms;
}