wolfssl-ra-challenger.c

/**
 * wolfSSL-based implementation of the RA-TLS challenger API
 * (cf. ra-challenger.h).
 */

#include <assert.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>

#include <wolfssl/options.h>
#include <wolfssl/ssl.h>
#include <wolfssl/wolfcrypt/asn.h>
#include <wolfssl/wolfcrypt/asn_public.h>
#include <wolfssl/wolfcrypt/coding.h>
#include <wolfssl/wolfcrypt/rsa.h>
#include <wolfssl/wolfcrypt/sha256.h>
#include <wolfssl/wolfcrypt/signature.h>

#ifdef RATLS_ECDSA
#include <SgxEcdsaAttestation/QuoteVerification.h>
#endif

#include "ra.h"
#include "wolfssl-ra.h"
#include "ra-challenger.h"
#include "ra-challenger_private.h"

#ifdef RATLS_ECDSA
#include "ecdsa-sample-data/real/sample_data.h"
#endif

extern unsigned char ias_sign_ca_cert_der[];
extern unsigned int ias_sign_ca_cert_der_len;

void get_quote_from_cert
(
    const uint8_t* der_crt,
    uint32_t der_crt_len,
    sgx_quote_t* q
)
{
    DecodedCert crt;
    int ret;

    InitDecodedCert(&crt, (byte*) der_crt, der_crt_len, NULL);
    InitSignatureCtx(&crt.sigCtx, NULL, INVALID_DEVID);
    ret = ParseCertRelative(&crt, CERT_TYPE, NO_VERIFY, 0);
    assert(ret == 0);
    
    get_quote_from_extension(crt.extensions, crt.extensionsSz, q);

    FreeDecodedCert(&crt);
}

void get_quote_from_report
(
    const uint8_t* report /* in */,
    const int report_len  /* in */,
    sgx_quote_t* quote
)
{
    // Move report into \0 terminated buffer such that we can work
    // with str* functions.
    char buf[report_len + 1];
    memcpy(buf, report, report_len);
    buf[report_len] = '\0';

    const char* json_string = "\"isvEnclaveQuoteBody\":\"";
    char* p_begin = strstr(buf, json_string);
    assert(p_begin != NULL);
    p_begin += strlen(json_string);
    const char* p_end = strchr(p_begin, '"');
    assert(p_end != NULL);

    const int quote_base64_len = p_end - p_begin;
    uint8_t* quote_bin = malloc(quote_base64_len);
    uint32_t quote_bin_len = quote_base64_len;

    Base64_Decode((const byte*) p_begin, quote_base64_len,
                  quote_bin, &quote_bin_len);
    
    assert(quote_bin_len <= sizeof(sgx_quote_t));
    memset(quote, 0, sizeof(sgx_quote_t));
    memcpy(quote, quote_bin, quote_bin_len);
    free(quote_bin);
}

static
int verify_report_data_against_server_cert
(
    DecodedCert* crt,
    sgx_quote_t* quote
)
{
    /* crt->publicKey seems to be the DER encoded public key. The
       OpenSSL DER formatted version of the public key obtained with
       openssl rsa -in ./server-key.pem -pubout -outform DER -out
       server-pubkey.der has an additional 24 bytes
       prefix/header. d->pubKeySize is 270 and the server-pubkey.der
       file has 294 bytes. That's to be expected according to [1] */
    /* [1] https://crypto.stackexchange.com/questions/14491/why-is-a-2048-bit-public-rsa-key-represented-by-540-hexadecimal-characters-in  */
    
    /* 2017-12-06, Thomas Knauth, A hard-coded offset into the
       DER-encoded public key only works for specific key sizes. The
       24 byte offset is specific to 2048 bit RSA keys. For example, a
       1024 bit RSA key only has an offset of 22.
 */
    RsaKey rsaKey;
    unsigned int idx = 0;
    int ret;
    
    wc_InitRsaKey(&rsaKey, NULL);
    ret = wc_RsaPublicKeyDecode(crt->publicKey, &idx, &rsaKey, crt->pubKeySize);
    assert(ret == 0);
    
    byte shaSum[SHA256_DIGEST_SIZE] = {0, };
    sha256_rsa_pubkey(shaSum, &rsaKey);
    wc_FreeRsaKey(&rsaKey);

#ifdef DEBUG
    fprintf(stderr, "SHA256 of server's public key:\n");
    for (int i=0; i < SHA256_DIGEST_SIZE; ++i) fprintf(stderr, "%02x", shaSum[i]);
    fprintf(stderr, "\n");

    fprintf(stderr, "Quote's report data:\n");
    for (int i=0; i < SGX_REPORT_DATA_SIZE; ++i) fprintf(stderr, "%02x", quote->report_body.report_data.d[i]);
    fprintf(stderr, "\n");
#endif
    
    assert(SHA256_DIGEST_SIZE <= SGX_REPORT_DATA_SIZE);
    ret = memcmp(quote->report_body.report_data.d, shaSum, SHA256_DIGEST_SIZE);
    assert(ret == 0);

    return ret;
}

static
int verify_ias_report_signature
(
    attestation_verification_report_t* attn_report
)
{
    DecodedCert crt;
    int ret;

    uint8_t der[4096];
    int der_len;
    der_len = wolfSSL_CertPemToDer(attn_report->ias_sign_cert, attn_report->ias_sign_cert_len,
                                   der, sizeof(der),
                                   CERT_TYPE);
    assert(der_len > 0);
    
    InitDecodedCert(&crt, der, der_len, NULL);
    InitSignatureCtx(&crt.sigCtx, NULL, INVALID_DEVID);
    ret = ParseCertRelative(&crt, CERT_TYPE, NO_VERIFY, 0);
    assert(ret == 0);

    RsaKey rsaKey;
    unsigned int idx = 0;
    
    ret = wc_InitRsaKey(&rsaKey, NULL);
    assert(ret == 0);
    ret = wc_RsaPublicKeyDecode(crt.publicKey, &idx, &rsaKey, crt.pubKeySize);
    assert(ret == 0);

    ret = wc_SignatureVerify(WC_HASH_TYPE_SHA256,
                             /* This is required such that signature
                                matches what OpenSSL produces. OpenSSL
                                embeds the hash in an ASN.1 structure
                                before signing it. */
                             WC_SIGNATURE_TYPE_RSA_W_ENC,
                             attn_report->ias_report, attn_report->ias_report_len,
                             attn_report->ias_report_signature, attn_report->ias_report_signature_len,
                             &rsaKey, sizeof(rsaKey));

    FreeDecodedCert(&crt);
    wc_FreeRsaKey(&rsaKey);

    return ret;
}

static
int verify_ias_certificate_chain(attestation_verification_report_t* attn_report) {
    WOLFSSL_CERT_MANAGER* cm;

    cm = wolfSSL_CertManagerNew();
    assert(cm != NULL);

    /* like load verify locations, 1 for success, < 0 for error */
    int ret = wolfSSL_CertManagerLoadCABuffer(cm, ias_sign_ca_cert_der,
                                              ias_sign_ca_cert_der_len,
                                              SSL_FILETYPE_ASN1);
    assert(ret == 1);
    
    ret = wolfSSL_CertManagerVerifyBuffer(cm, attn_report->ias_sign_cert,
                                          attn_report->ias_sign_cert_len,
                                          SSL_FILETYPE_PEM);
    assert(ret == SSL_SUCCESS);
    
    wolfSSL_CertManagerFree(cm);
    cm = NULL;
    
    return 0;
}

/**
 * Check if isvEnclaveQuoteStatus is "OK"
 * (cf. https://software.intel.com/sites/default/files/managed/7e/3b/ias-api-spec.pdf,
 * pg. 24).
 *
 * @return 0 if verified successfully, 1 otherwise.
 */
static
int verify_enclave_quote_status
(
    const char* ias_report,
    int   ias_report_len
)
{
    // Move ias_report into \0 terminated buffer such that we can work
    // with str* functions.
    char buf[ias_report_len + 1];
    memcpy(buf, ias_report, ias_report_len);
    buf[ias_report_len] = '\0';
    
    const char* json_string = "\"isvEnclaveQuoteStatus\":\"";
    char* p_begin = strstr(buf, json_string);
    assert(p_begin != NULL);
    p_begin += strlen(json_string);

    const char* status_OK = "OK\"";
    if (0 == strncmp(p_begin, status_OK, strlen(status_OK))) return 0;
#ifdef SGX_GROUP_OUT_OF_DATE
    const char* status_outdated = "GROUP_OUT_OF_DATE\"";
    if (0 == strncmp(p_begin, status_outdated, strlen(status_outdated))) {
        printf("WARNING: isvEnclaveQuoteStatus is GROUP_OUT_OF_DATE\n");
        return 0;
    }
#endif
    return 1;
}

static
int epid_verify_sgx_cert_extensions
(
    uint8_t* der_crt,
    uint32_t der_crt_len
)
{
    attestation_verification_report_t attn_report;

    DecodedCert crt;
    int ret;

    InitDecodedCert(&crt, der_crt, der_crt_len, NULL);
    InitSignatureCtx(&crt.sigCtx, NULL, INVALID_DEVID);
    ret = ParseCertRelative(&crt, CERT_TYPE, NO_VERIFY, 0);
    assert(ret == 0);
    
    extract_x509_extensions(crt.extensions, crt.extensionsSz, &attn_report);

    /* Base64 decode attestation report signature. */
    uint8_t sig_base64[sizeof(attn_report.ias_report_signature)];
    memcpy(sig_base64, attn_report.ias_report_signature, attn_report.ias_report_signature_len);
    int rc = Base64_Decode(sig_base64, attn_report.ias_report_signature_len,
                           attn_report.ias_report_signature, &attn_report.ias_report_signature_len);
    assert(0 == rc);
    
    ret = verify_ias_certificate_chain(&attn_report);
    assert(ret == 0);

    ret = verify_ias_report_signature(&attn_report);
    assert(ret == 0);

    ret = verify_enclave_quote_status((const char*) attn_report.ias_report,
                                      attn_report.ias_report_len);
    assert(ret == 0);
    
    sgx_quote_t quote = {0, };
    get_quote_from_report(attn_report.ias_report,
                          attn_report.ias_report_len,
                          &quote);
    ret = verify_report_data_against_server_cert(&crt, &quote);
    assert(ret == 0);

    FreeDecodedCert(&crt);

    return 0;
}

#ifdef RATLS_ECDSA
static
int ecdsa_verify_sgx_cert_extensions
(
    uint8_t* der_crt,
    uint32_t der_crt_len
)
{
    DecodedCert crt;
    int ret;

    InitDecodedCert(&crt, der_crt, der_crt_len, NULL);
    InitSignatureCtx(&crt.sigCtx, NULL, INVALID_DEVID);
    ret = ParseCertRelative(&crt, CERT_TYPE, NO_VERIFY, 0);
    assert(ret == 0);

    ecdsa_attestation_evidence_t evidence;
    ecdsa_extract_x509_extensions(crt.extensions,
                                  crt.extensionsSz,
                                  &evidence);
    FreeDecodedCert(&crt);

    /* pem_cert_chain := pck cert + pck CA cert + root CA cert */
    /* crls := root ca crl + pck crl */
    /* pem_trusted_root_ca_cert */
    size_t pck_cert_chain_len = evidence.pck_sign_chain_len + evidence.pck_crt_len + 1;
    char pck_cert_chain[pck_cert_chain_len];
    memcpy(pck_cert_chain, evidence.pck_crt, evidence.pck_crt_len);
    memcpy(pck_cert_chain + evidence.pck_crt_len, evidence.pck_sign_chain, evidence.pck_sign_chain_len);
    pck_cert_chain[sizeof(pck_cert_chain) - 1] = '\0';

    assert(evidence.root_ca_crl_len < sizeof(evidence.root_ca_crl));
    evidence.root_ca_crl[evidence.root_ca_crl_len] = '\0';
    assert(evidence.pck_crl_len < sizeof(evidence.pck_crl));
    evidence.pck_crl[evidence.pck_crl_len] = '\0';

    const char* const crls[] = {(char*) evidence.root_ca_crl,
                                (char*) evidence.pck_crl};

    /* SGXDataCenterAttestationPrimitives/QuoteVerification/Src/ThirdParty/CMakeLists.txt depends on openssl-1.1.0i.tar.gz" */
    /* libQuoteVerification.so seems to link in OpenSSL dependencies statically?! */

    /* QVL expects zero terminated strings as input! */

    int pck_crt_status = sgxAttestationVerifyPCKCertificate(pck_cert_chain, crls,
                                                            (char*) ecdsa_sample_data_real_trustedRootCaCert_pem);

    assert(evidence.tcb_info_len < sizeof(evidence.tcb_info));
    evidence.tcb_info[evidence.tcb_info_len] = '\0';
    assert(evidence.tcb_sign_chain_len < sizeof(evidence.tcb_sign_chain));
    evidence.tcb_sign_chain[evidence.tcb_sign_chain_len] = '\0';
    int tcb_info_status = sgxAttestationVerifyTCBInfo((char*) evidence.tcb_info,
                                                      (char*) evidence.tcb_sign_chain,
                                                      (char*) evidence.root_ca_crl,
                                                      (char*) ecdsa_sample_data_real_trustedRootCaCert_pem);

    assert(evidence.qe_identity_len < sizeof(evidence.qe_identity));
    evidence.qe_identity[evidence.qe_identity_len] = '\0';

    int qe_identity_status = sgxAttestationVerifyQEIdentity((char*) evidence.qe_identity,
                                                            (char*) evidence.tcb_sign_chain,
                                                            (char*) evidence.root_ca_crl,
                                                            (char*) ecdsa_sample_data_real_trustedRootCaCert_pem);

    int quote_status = sgxAttestationVerifyQuote(evidence.quote, evidence.quote_len,
                                                 (char*) evidence.pck_crt,
                                                 (char*) evidence.pck_crl,
                                                 (char*) evidence.tcb_info,
                                                 (char*) evidence.qe_identity);

    // TODO Update DCAP SDK to newest version.
    if (quote_status == STATUS_TCB_OUT_OF_DATE) {
        printf("!!! WARNING: quote verification resulted in STATUS_TCB_OUT_OF_DATE\n");
        quote_status = 0;
    }

    int report_user_data_status = verify_report_data_against_server_cert(&crt, (sgx_quote_t*) evidence.quote);

    return pck_crt_status || tcb_info_status || qe_identity_status || quote_status || report_user_data_status;
}
#endif

int verify_sgx_cert_extensions
(
    uint8_t* der_crt,
    uint32_t der_crt_len
)
{
    if (is_epid_ratls_cert(der_crt, der_crt_len)) {
        return epid_verify_sgx_cert_extensions(der_crt, der_crt_len);
    } else {
#ifdef RATLS_ECDSA
        return ecdsa_verify_sgx_cert_extensions(der_crt, der_crt_len);
#endif
    }
    assert(0);
    // Avoid compiler error: control reaches end of non-void function
    // [-Werror=return-type]
    return -1;
}