/*
 * Copyright (c) 2021 Yubico AB. All rights reserved.
 * Use of this source code is governed by a BSD-style
 * license that can be found in the LICENSE file.
 */

/*
 * Trusted Platform Module (TPM) 2.0 attestation support. Documentation
 * references are relative to revision 01.38 of the TPM 2.0 specification.
 */

#include <openssl/sha.h>

#include "packed.h"
#include "fido.h"

/* Part 1, 4.89: TPM_GENERATED_VALUE */
#define TPM_MAGIC       0xff544347

/* Part 2, 6.3: TPM_ALG_ID */
#define TPM_ALG_RSA     0x0001
#define TPM_ALG_SHA256  0x000b
#define TPM_ALG_NULL    0x0010
#define TPM_ALG_ECC     0x0023

/* Part 2, 6.4: TPM_ECC_CURVE */
#define TPM_ECC_P256    0x0003

/* Part 2, 6.9: TPM_ST_ATTEST_CERTIFY */
#define TPM_ST_CERTIFY  0x8017

/* Part 2, 8.3: TPMA_OBJECT */
#define TPMA_RESERVED   0xfff8f309      /* reserved bits; must be zero */
#define TPMA_FIXED      0x00000002      /* object has fixed hierarchy */
#define TPMA_CLEAR      0x00000004      /* object persists */
#define TPMA_FIXED_P    0x00000010      /* object has fixed parent */
#define TPMA_SENSITIVE  0x00000020      /* data originates within tpm */
#define TPMA_SIGN       0x00040000      /* object may sign */

/* Part 2, 10.4.2: TPM2B_DIGEST */
PACKED_TYPE(tpm_sha256_digest_t,
struct tpm_sha256_digest {
        uint16_t size; /* sizeof(body) */
        uint8_t  body[32];
})

/* Part 2, 10.4.3: TPM2B_DATA */
PACKED_TYPE(tpm_sha1_data_t,
struct tpm_sha1_data {
        uint16_t size; /* sizeof(body */
        uint8_t  body[20];
})

/* Part 2, 10.5.3: TPM2B_NAME */
PACKED_TYPE(tpm_sha256_name_t,
struct tpm_sha256_name {
        uint16_t size; /* sizeof(alg) + sizeof(body) */
        uint16_t alg;  /* TPM_ALG_SHA256 */
        uint8_t  body[32];
})

/* Part 2, 10.11.1: TPMS_CLOCK_INFO */
PACKED_TYPE(tpm_clock_info_t,
struct tpm_clock_info {
        uint64_t timestamp_ms;
        uint32_t reset_count;   /* obfuscated by tpm */
        uint32_t restart_count; /* obfuscated by tpm */
        uint8_t  safe;          /* 1 if timestamp_ms is current */
})

/* Part 2, 10.12.8 TPMS_ATTEST */
PACKED_TYPE(tpm_sha1_attest_t,
struct tpm_sha1_attest {
        uint32_t          magic;     /* TPM_MAGIC */
        uint16_t          type;      /* TPM_ST_ATTEST_CERTIFY */
        tpm_sha256_name_t signer;    /* full tpm path of signing key */
        tpm_sha1_data_t   data;      /* signed sha1 */
        tpm_clock_info_t  clock;
        uint64_t          fwversion; /* obfuscated by tpm */
        tpm_sha256_name_t name;      /* sha256 of tpm_rs256_pubarea_t */
        tpm_sha256_name_t qual_name; /* full tpm path of attested key */
})

/* Part 2, 11.2.4.5: TPM2B_PUBLIC_KEY_RSA */
PACKED_TYPE(tpm_rs256_key_t,
struct tpm_rs256_key {
        uint16_t size; /* sizeof(body) */
        uint8_t  body[256];
})

/* Part 2, 11.2.5.1: TPM2B_ECC_PARAMETER */
PACKED_TYPE(tpm_es256_coord_t,
struct tpm_es256_coord {
        uint16_t size; /* sizeof(body) */
        uint8_t  body[32];
})

/* Part 2, 11.2.5.2: TPMS_ECC_POINT */
PACKED_TYPE(tpm_es256_point_t,
struct tpm_es256_point {
        tpm_es256_coord_t x;
        tpm_es256_coord_t y;
})

/* Part 2, 12.2.3.5: TPMS_RSA_PARMS */
PACKED_TYPE(tpm_rs256_param_t,
struct tpm_rs256_param {
        uint16_t symmetric; /* TPM_ALG_NULL */
        uint16_t scheme;    /* TPM_ALG_NULL */
        uint16_t keybits;   /* 2048 */
        uint32_t exponent;  /* zero (meaning 2^16 + 1) */
})

/* Part 2, 12.2.3.6: TPMS_ECC_PARMS */
PACKED_TYPE(tpm_es256_param_t,
struct tpm_es256_param {
        uint16_t symmetric; /* TPM_ALG_NULL */
        uint16_t scheme;    /* TPM_ALG_NULL */
        uint16_t curve_id;  /* TPM_ECC_P256 */
        uint16_t kdf;       /* TPM_ALG_NULL */
})

/* Part 2, 12.2.4: TPMT_PUBLIC */
PACKED_TYPE(tpm_rs256_pubarea_t,
struct tpm_rs256_pubarea {
        uint16_t            alg;    /* TPM_ALG_RSA */
        uint16_t            hash;   /* TPM_ALG_SHA256 */
        uint32_t            attr;
        tpm_sha256_digest_t policy; /* must be present? */
        tpm_rs256_param_t   param;
        tpm_rs256_key_t     key;
})

/* Part 2, 12.2.4: TPMT_PUBLIC */
PACKED_TYPE(tpm_es256_pubarea_t,
struct tpm_es256_pubarea {
        uint16_t            alg;    /* TPM_ALG_ECC */
        uint16_t            hash;   /* TPM_ALG_SHA256 */
        uint32_t            attr;
        tpm_sha256_digest_t policy; /* must be present? */
        tpm_es256_param_t   param;
        tpm_es256_point_t   point;
})

static int
get_signed_sha1(tpm_sha1_data_t *dgst, const fido_blob_t *authdata,
    const fido_blob_t *clientdata)
{
        const EVP_MD    *md = NULL;
        EVP_MD_CTX      *ctx = NULL;
        int              ok = -1;

        if ((dgst->size = sizeof(dgst->body)) != SHA_DIGEST_LENGTH ||
            (md = EVP_sha1()) == NULL ||
            (ctx = EVP_MD_CTX_new()) == NULL ||
            EVP_DigestInit_ex(ctx, md, NULL) != 1 ||
            EVP_DigestUpdate(ctx, authdata->ptr, authdata->len) != 1 ||
            EVP_DigestUpdate(ctx, clientdata->ptr, clientdata->len) != 1 ||
            EVP_DigestFinal_ex(ctx, dgst->body, NULL) != 1) {
                fido_log_debug("%s: sha1", __func__);
                goto fail;
        }

        ok = 0;
fail:
        EVP_MD_CTX_free(ctx);

        return (ok);
}

static int
get_signed_name(tpm_sha256_name_t *name, const fido_blob_t *pubarea)
{
        name->alg = TPM_ALG_SHA256;
        name->size = sizeof(name->alg) + sizeof(name->body);
        if (sizeof(name->body) != SHA256_DIGEST_LENGTH ||
            SHA256(pubarea->ptr, pubarea->len, name->body) != name->body) {
                fido_log_debug("%s: sha256", __func__);
                return -1;
        }

        return 0;
}

static void
bswap_rs256_pubarea(tpm_rs256_pubarea_t *x)
{
        x->alg = htobe16(x->alg);
        x->hash = htobe16(x->hash);
        x->attr = htobe32(x->attr);
        x->policy.size = htobe16(x->policy.size);
        x->param.symmetric = htobe16(x->param.symmetric);
        x->param.scheme = htobe16(x->param.scheme);
        x->param.keybits = htobe16(x->param.keybits);
        x->key.size = htobe16(x->key.size);
}

static void
bswap_es256_pubarea(tpm_es256_pubarea_t *x)
{
        x->alg = htobe16(x->alg);
        x->hash = htobe16(x->hash);
        x->attr = htobe32(x->attr);
        x->policy.size = htobe16(x->policy.size);
        x->param.symmetric = htobe16(x->param.symmetric);
        x->param.scheme = htobe16(x->param.scheme);
        x->param.curve_id = htobe16(x->param.curve_id);
        x->param.kdf = htobe16(x->param.kdf);
        x->point.x.size = htobe16(x->point.x.size);
        x->point.y.size = htobe16(x->point.y.size);
}

static void
bswap_sha1_certinfo(tpm_sha1_attest_t *x)
{
        x->magic = htobe32(x->magic);
        x->type = htobe16(x->type);
        x->signer.size = htobe16(x->signer.size);
        x->data.size = htobe16(x->data.size);
        x->name.alg = htobe16(x->name.alg);
        x->name.size = htobe16(x->name.size);
}

static int
check_rs256_pubarea(const fido_blob_t *buf, const rs256_pk_t *pk)
{
        const tpm_rs256_pubarea_t       *actual;
        tpm_rs256_pubarea_t              expected;
        int                              ok;

        if (buf->len != sizeof(*actual)) {
                fido_log_debug("%s: buf->len=%zu", __func__, buf->len);
                return -1;
        }
        actual = (const void *)buf->ptr;

        memset(&expected, 0, sizeof(expected));
        expected.alg = TPM_ALG_RSA;
        expected.hash = TPM_ALG_SHA256;
        expected.attr = be32toh(actual->attr);
        expected.attr &= ~(TPMA_RESERVED|TPMA_CLEAR);
        expected.attr |= (TPMA_FIXED|TPMA_FIXED_P|TPMA_SENSITIVE|TPMA_SIGN);
        expected.policy = actual->policy;
        expected.policy.size = sizeof(expected.policy.body);
        expected.param.symmetric = TPM_ALG_NULL;
        expected.param.scheme = TPM_ALG_NULL;
        expected.param.keybits = 2048;
        expected.param.exponent = 0; /* meaning 2^16+1 */
        expected.key.size = sizeof(expected.key.body);
        memcpy(&expected.key.body, &pk->n, sizeof(expected.key.body));
        bswap_rs256_pubarea(&expected);

        ok = timingsafe_bcmp(&expected, actual, sizeof(expected));
        explicit_bzero(&expected, sizeof(expected));

        return ok != 0 ? -1 : 0;
}

static int
check_es256_pubarea(const fido_blob_t *buf, const es256_pk_t *pk)
{
        const tpm_es256_pubarea_t       *actual;
        tpm_es256_pubarea_t              expected;
        int                              ok;

        if (buf->len != sizeof(*actual)) {
                fido_log_debug("%s: buf->len=%zu", __func__, buf->len);
                return -1;
        }
        actual = (const void *)buf->ptr;

        memset(&expected, 0, sizeof(expected));
        expected.alg = TPM_ALG_ECC;
        expected.hash = TPM_ALG_SHA256;
        expected.attr = be32toh(actual->attr);
        expected.attr &= ~(TPMA_RESERVED|TPMA_CLEAR);
        expected.attr |= (TPMA_FIXED|TPMA_FIXED_P|TPMA_SENSITIVE|TPMA_SIGN);
        expected.policy = actual->policy;
        expected.policy.size = sizeof(expected.policy.body);
        expected.param.symmetric = TPM_ALG_NULL;
        expected.param.scheme = TPM_ALG_NULL; /* TCG Alg. Registry, 5.2.4 */
        expected.param.curve_id = TPM_ECC_P256;
        expected.param.kdf = TPM_ALG_NULL;
        expected.point.x.size = sizeof(expected.point.x.body);
        expected.point.y.size = sizeof(expected.point.y.body);
        memcpy(&expected.point.x.body, &pk->x, sizeof(expected.point.x.body));
        memcpy(&expected.point.y.body, &pk->y, sizeof(expected.point.y.body));
        bswap_es256_pubarea(&expected);

        ok = timingsafe_bcmp(&expected, actual, sizeof(expected));
        explicit_bzero(&expected, sizeof(expected));

        return ok != 0 ? -1 : 0;
}

static int
check_sha1_certinfo(const fido_blob_t *buf, const fido_blob_t *clientdata_hash,
    const fido_blob_t *authdata_raw, const fido_blob_t *pubarea)
{
        const tpm_sha1_attest_t *actual;
        tpm_sha1_attest_t        expected;
        tpm_sha1_data_t          signed_data;
        tpm_sha256_name_t        signed_name;
        int                      ok = -1;

        memset(&signed_data, 0, sizeof(signed_data));
        memset(&signed_name, 0, sizeof(signed_name));

        if (get_signed_sha1(&signed_data, authdata_raw, clientdata_hash) < 0 ||
            get_signed_name(&signed_name, pubarea) < 0) {
                fido_log_debug("%s: get_signed_sha1/name", __func__);
                goto fail;
        }
        if (buf->len != sizeof(*actual)) {
                fido_log_debug("%s: buf->len=%zu", __func__, buf->len);
                goto fail;
        }
        actual = (const void *)buf->ptr;

        memset(&expected, 0, sizeof(expected));
        expected.magic = TPM_MAGIC;
        expected.type = TPM_ST_CERTIFY;
        expected.signer = actual->signer;
        expected.signer.size = sizeof(expected.signer.alg) +
            sizeof(expected.signer.body);
        expected.data = signed_data;
        expected.clock = actual->clock;
        expected.clock.safe = 1;
        expected.fwversion = actual->fwversion;
        expected.name = signed_name;
        expected.qual_name = actual->qual_name;
        bswap_sha1_certinfo(&expected);

        ok = timingsafe_bcmp(&expected, actual, sizeof(expected));
fail:
        explicit_bzero(&expected, sizeof(expected));
        explicit_bzero(&signed_data, sizeof(signed_data));
        explicit_bzero(&signed_name, sizeof(signed_name));

        return ok != 0 ? -1 : 0;
}

int
fido_get_signed_hash_tpm(fido_blob_t *dgst, const fido_blob_t *clientdata_hash,
    const fido_blob_t *authdata_raw, const fido_attstmt_t *attstmt,
    const fido_attcred_t *attcred)
{
        const fido_blob_t *pubarea = &attstmt->pubarea;
        const fido_blob_t *certinfo = &attstmt->certinfo;

        if (attstmt->alg != COSE_RS1) {
                fido_log_debug("%s: unsupported alg %d", __func__,
                    attstmt->alg);
                return -1;
        }

        switch (attcred->type) {
        case COSE_ES256:
                if (check_es256_pubarea(pubarea, &attcred->pubkey.es256) < 0) {
                        fido_log_debug("%s: check_es256_pubarea", __func__);
                        return -1;
                }
                break;
        case COSE_RS256:
                if (check_rs256_pubarea(pubarea, &attcred->pubkey.rs256) < 0) {
                        fido_log_debug("%s: check_rs256_pubarea", __func__);
                        return -1;
                }
                break;
        default:
                fido_log_debug("%s: unsupported type %d", __func__,
                    attcred->type);
                return -1;
        }

        if (check_sha1_certinfo(certinfo, clientdata_hash, authdata_raw,
            pubarea) < 0) {
                fido_log_debug("%s: check_sha1_certinfo", __func__);
                return -1;
        }

        if (dgst->len < SHA_DIGEST_LENGTH ||
            SHA1(certinfo->ptr, certinfo->len, dgst->ptr) != dgst->ptr) {
                fido_log_debug("%s: sha1", __func__);
                return -1;
        }
        dgst->len = SHA_DIGEST_LENGTH;

        return 0;
}