/* SPDX-License-Identifier: GPL-2.0 */

/** \file openssl.c Openssl-based encryption/decryption routines. */

#include <sys/types.h>
#include <sys/socket.h>
#include <openssl/rand.h>
#include <openssl/err.h>
#include <openssl/pem.h>
#include <openssl/sha.h>
#include <openssl/bn.h>
#include <openssl/aes.h>
#include <openssl/evp.h>

#include "para.h"
#include "error.h"
#include "string.h"
#include "crypt.h"
#include "crypt_backend.h"
#include "portable_io.h"

struct asymmetric_key {
	RSA *rsa;
	EVP_PKEY *pkey;
	EVP_PKEY_CTX *ctx;
};

static int openssl_perror(const char *pfx)
{
	unsigned long err = ERR_get_error();
	PARA_ERROR_LOG("%s: \"%s\"\n", pfx, ERR_reason_error_string(err));
	return -E_OPENSSL;
}

void get_random_bytes_or_die(unsigned char *buf, int num)
{
	int ret;

	if (RAND_bytes(buf, num) == 1) /* success */
		return;
	ret = openssl_perror("RAND_bytes");
	PARA_EMERG_LOG("%s\n", strerror(-ret));
	exit(EXIT_FAILURE);
}

/*
 * Read 64 bytes from /dev/urandom and add them to the SSL PRNG. Then seed the
 * PRNG used by random(3) with a random seed obtained from SSL.
 */
void crypt_init(void)
{
	int seed, ret = RAND_load_file("/dev/urandom", 64);

	if (ret != 64) {
		PARA_EMERG_LOG("could not seed PRNG (ret = %d)\n", ret);
		exit(EXIT_FAILURE);
	}
	get_random_bytes_or_die((unsigned char *)&seed, sizeof(seed));
	srandom(seed);
}

void crypt_shutdown(void)
{
	OPENSSL_thread_stop();
	EVP_cleanup();
}

/*
 * The public key loading functions below were inspired by corresponding code
 * of openssh-5.2p1, Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo,
 * Finland. However, not much of the original code remains.
 */

static int read_bignum(const unsigned char *buf, size_t len, BIGNUM **result)
{
	const unsigned char *p = buf, *end = buf + len;
	uint32_t bnsize;
	BIGNUM *bn;

	if (p + 4 < p)
		return -E_BIGNUM;
	if (p + 4 > end)
		return -E_BIGNUM;
	bnsize = read_u32_be(p);
	PARA_DEBUG_LOG("bnsize: %u\n", bnsize);
	p += 4;
	if (p + bnsize < p)
		return -E_BIGNUM;
	if (p + bnsize > end)
		return -E_BIGNUM;
	if (bnsize > 8192)
		return -E_BIGNUM;
	bn = BN_bin2bn(p, bnsize, NULL);
	if (!bn)
		return -E_BIGNUM;
	*result = bn;
	return bnsize + 4;
}

#ifdef HAVE_OSSL_PARAM /* openssl-3 */

static int generate_private_pkey(struct asymmetric_key *priv,
		const BIGNUM *n, const BIGNUM *e, const BIGNUM *d,
		const BIGNUM *p, const BIGNUM *q)
{
	const BIGNUM *bignums[] = {n, e, d, p, q};
	const char *strings[] = {"n", "e", "d", "p", "q"};
	int ret, bytes[ARRAY_SIZE(bignums)];
	unsigned char *bufs[ARRAY_SIZE(bignums)];
	OSSL_PARAM params[ARRAY_SIZE(bignums) + 1];
	/*
	 * Convert bignums to buffers for OSSL_PARAM_construct_BN() and init
	 * params[].
	 */
	for (int i = 0; i < ARRAY_SIZE(bignums); i++) {
		bytes[i] = BN_num_bytes(bignums[i]);
		PARA_DEBUG_LOG("%s: %d bits\n", strings[i], bytes[i] * 8);
		bufs[i] = alloc(bytes[i]);
		assert(BN_bn2nativepad(bignums[i], bufs[i], bytes[i]) > 0);
		params[i] = OSSL_PARAM_construct_BN(strings[i], bufs[i],
			bytes[i]);
	}
	params[ARRAY_SIZE(bignums)] = OSSL_PARAM_construct_end();
	/* Transfer buffers to openssl to create the pkey from it */
	priv->ctx = EVP_PKEY_CTX_new_from_name(NULL, "RSA", NULL);
	assert(priv->ctx);
	assert(EVP_PKEY_fromdata_init(priv->ctx) > 0);
	ret = EVP_PKEY_fromdata(priv->ctx, &priv->pkey,
		EVP_PKEY_KEYPAIR, params);
	for (int i = 0; i < ARRAY_SIZE(bignums); i++)
		free(bufs[i]);
	if (ret <= 0) {
		EVP_PKEY_CTX_free(priv->ctx);
		return openssl_perror("EVP_PKEY_fromdata()");
	}
	assert(priv->pkey);
	return BN_num_bytes(n) * 8;
}

/*
 * Convert bignumns e and n to a pkey and context.
 */
static int generate_public_pkey(struct asymmetric_key *pub,
		const BIGNUM *e, const BIGNUM *n)
{
	unsigned char *ebuf, *nbuf;
	int ret, ebytes = BN_num_bytes(e), nbytes = BN_num_bytes(n);
	OSSL_PARAM params[3];

	/* Convert e and n to a buffer for OSSL_PARAM_construct_BN() */
	ebuf = alloc(ebytes);
	assert(BN_bn2nativepad(e, ebuf, ebytes) > 0);
	nbuf = alloc(nbytes);
	assert(BN_bn2nativepad(n, nbuf, nbytes) > 0);
	/* Init params[] with {e,n}buf and create the pkey from it */
	params[0] = OSSL_PARAM_construct_BN("e", ebuf, ebytes);
	params[1] = OSSL_PARAM_construct_BN("n", nbuf, nbytes);
	params[2] = OSSL_PARAM_construct_end();
	pub->ctx = EVP_PKEY_CTX_new_from_name(NULL, "RSA", NULL);
	assert(pub->ctx);
	assert(EVP_PKEY_fromdata_init(pub->ctx) > 0);
	ret = EVP_PKEY_fromdata(pub->ctx, &pub->pkey, EVP_PKEY_PUBLIC_KEY,
		params);
	free(nbuf);
	free(ebuf);
	if (ret <= 0) {
		EVP_PKEY_CTX_free(pub->ctx);
		return openssl_perror("EVP_PKEY_fromdata()");
	}
	assert(pub->pkey);
	return nbytes * 8;
}

#endif /* HAVE_OSSL_PARAM */

static int read_public_key(const unsigned char *blob, size_t blen,
		struct asymmetric_key *pub)
{
	int ret, bits;
	const unsigned char *p = blob, *end = blob + blen;
	BIGNUM *e, *n;

	ret = read_bignum(p, end - p, &e);
	if (ret < 0)
		return ret;
	p += ret;
	ret = read_bignum(p, end - p, &n);
	if (ret < 0) {
		BN_free(e);
		return ret;
	}
	bits = BN_num_bytes(n) * 8;
	PARA_DEBUG_LOG("modulus: %d bits\n", bits);
#ifdef HAVE_OSSL_PARAM /* openssl-3 */
	ret = generate_public_pkey(pub, e, n);
	BN_free(e);
	BN_free(n);
	if (ret < 0)
		return ret;
#else /* openssl < 3.0 */
	pub->rsa = RSA_new();
	assert(pub->rsa);
	RSA_set0_key(pub->rsa, n, e, NULL);
	/* e and n are now owned by openssl */
#endif /* HAVE_OSSL_PARAM */
	return bits;
}

static int read_openssh_private_key(const unsigned char *blob,
		const unsigned char *end, struct asymmetric_key *priv)
{
	int ret;
	BIGNUM *n, *e, *d, *iqmp, *p, *q; /* stored in the key file */
	const unsigned char *cp = blob;

	ret = read_bignum(cp, end - cp, &n);
	if (ret < 0)
		return ret;
	cp += ret;
	ret = read_bignum(cp, end - cp, &e);
	if (ret < 0)
		goto free_n;
	cp += ret;
	ret = read_bignum(cp, end - cp, &d);
	if (ret < 0)
		goto free_e;
	cp += ret;
	ret = read_bignum(cp, end - cp, &iqmp);
	if (ret < 0)
		goto free_d;
	cp += ret;
	ret = read_bignum(cp, end - cp, &p);
	if (ret < 0)
		goto free_iqmp;
	cp += ret;
	ret = read_bignum(cp, end - cp, &q);
	if (ret < 0)
		goto free_p;
#ifdef HAVE_OSSL_PARAM /* openssl-3 */
	/*
	 * Ignore iqmp, the coefficient for the Chinese remainder theorem. It is
	 * dispensable because it can be derived from the other values. Passing
	 * it to the EVP API results in a memory leak.
	 */
	ret = generate_private_pkey(priv, n, e, d, p, q);
#else
	assert((priv->rsa = RSA_new()));
	RSA_set0_key(priv->rsa, n, e, d);
	RSA_set0_factors(priv->rsa, p, q);
	RSA_set0_crt_params(priv->rsa, NULL, NULL, iqmp);
	BN_clear_free(iqmp); /* This is not freed by RSA_free() */
	return 1;
#endif /* HAVE_OSSL_PARAM */
	BN_clear_free(q);
free_p:
	BN_clear_free(p);
free_iqmp:
	BN_clear_free(iqmp);
free_d:
	BN_clear_free(d);
free_e:
	BN_free(e);
free_n:
	BN_free(n);
	return ret;
}

static int get_private_key(const char *path, struct asymmetric_key *priv)
{
	int ret;
	unsigned char *blob, *end;
	size_t blob_size;

	ret = decode_private_key(path, &blob, &blob_size);
	if (ret < 0)
		return ret;
	end = blob + blob_size;
	ret = find_openssh_bignum_offset(blob, blob_size);
	if (ret < 0)
		goto free_blob;
	PARA_INFO_LOG("reading RSA params at offset %d\n", ret);
	ret = read_openssh_private_key(blob + ret, end, priv);
free_blob:
	free(blob);
	return ret;
}

int apc_get_pubkey(const char *key_file, struct asymmetric_key **result)
{
	unsigned char *blob;
	size_t decoded_size;
	int ret;
	struct asymmetric_key *pub;

	ret = decode_public_key(key_file, &blob, &decoded_size);
	if (ret < 0)
		return ret;
	pub = zalloc(sizeof(*pub)); /* ->pkey needs to start out zeroed */
	ret = read_public_key(blob + ret, decoded_size - ret, pub);
	free(blob);
	if (ret < 0) {
		free(pub);
		*result = NULL;
		PARA_ERROR_LOG("can not load key %s\n", key_file);
		return ret;
	}
	PARA_NOTICE_LOG("loaded %d bit key from %s\n", ret, key_file);
	*result = pub;
	return ret / 8;
}

void apc_free_pubkey(struct asymmetric_key *pub)
{
	if (!pub)
		return;
#ifdef HAVE_OSSL_PARAM /* openssl-3 */
	EVP_PKEY_CTX_free(pub->ctx);
	EVP_PKEY_free(pub->pkey);
#else
	RSA_free(pub->rsa);
#endif
	free(pub);
}

#ifdef HAVE_OSSL_PARAM /* openssl-3 */
static int pkey_priv_decrypt(const struct asymmetric_key *priv,
		unsigned char **outbuf, unsigned char *inbuf, int inlen)
{
	EVP_PKEY_CTX *ctx;
	size_t outlen;

	assert((ctx = EVP_PKEY_CTX_new(priv->pkey, NULL)));
	assert((EVP_PKEY_decrypt_init(ctx) > 0));
	assert(EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_OAEP_PADDING) > 0);
	if (EVP_PKEY_decrypt(ctx, NULL, &outlen, inbuf, inlen) <= 0) {
		*outbuf = NULL;
		EVP_PKEY_CTX_free(ctx);
		return openssl_perror("EVP_PKEY_encrypt()");
	}
	*outbuf = alloc(outlen);
	assert((EVP_PKEY_decrypt(ctx, *outbuf, &outlen, inbuf, inlen) > 0));
	EVP_PKEY_CTX_free(ctx);
	PARA_INFO_LOG("wrote %zu decrypted data bytes\n", outlen);
	return outlen;
}
#endif /* HAVE_OSSL_PARAM */

int apc_priv_decrypt(const char *key_file, unsigned char **outbuf,
		unsigned char *inbuf, int inlen)
{
	struct asymmetric_key *priv;
	int ret;

	*outbuf = NULL;
	ret = check_private_key_file(key_file);
	if (ret < 0)
		return ret;
	if (inlen < 0)
		return -E_RSA;
	priv = zalloc(sizeof(*priv)); /* ->pkey needs to start out zeroed */
	ret = get_private_key(key_file, priv);
	if (ret < 0) {
		free(priv);
		return ret;
	}
#ifdef HAVE_OSSL_PARAM /* openssl-3 */
	ret = pkey_priv_decrypt(priv, outbuf, inbuf, inlen);
	EVP_PKEY_CTX_free(priv->ctx);
	EVP_PKEY_free(priv->pkey);
#else
	/*
	 * RSA is vulnerable to timing attacks. Generate a random blinding
	 * factor to protect against this kind of attack.
	 */
	ret = -E_BLINDING;
	if (RSA_blinding_on(priv->rsa, NULL) == 0)
		goto out;
	*outbuf = alloc(RSA_size(priv->rsa));
	ret = RSA_private_decrypt(inlen, inbuf, *outbuf, priv->rsa,
		RSA_PKCS1_OAEP_PADDING);
	RSA_blinding_off(priv->rsa);
	if (ret <= 0) {
		free(*outbuf);
		*outbuf = NULL;
		ret = -E_DECRYPT;
	}
out:
	RSA_free(priv->rsa);
#endif
	free(priv);
	return ret;
}

int apc_pub_encrypt(struct asymmetric_key *pub, unsigned char *inbuf,
		unsigned len, unsigned char **outbuf)
{
	int ret;
#ifdef HAVE_OSSL_PARAM /* openssl-3 */
	EVP_PKEY_CTX *ctx;
	size_t outlen;

	*outbuf = NULL;
	assert((ctx = EVP_PKEY_CTX_new(pub->pkey, NULL)));
	assert((EVP_PKEY_encrypt_init(ctx) > 0));
	assert((EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_OAEP_PADDING) > 0));
	if (EVP_PKEY_encrypt(ctx, NULL, &outlen, inbuf, len) <= 0) {
		ret = openssl_perror("EVP_PKEY_encrypt()");
		goto free_ctx;
	}
	*outbuf = alloc(outlen);
	assert((EVP_PKEY_encrypt(ctx, *outbuf, &outlen, inbuf, len) > 0));
	PARA_INFO_LOG("wrote %zu encrypted data bytes\n", outlen);
	ret = outlen;
free_ctx:
	EVP_PKEY_CTX_free(ctx);
	return ret;
#else /* openssl < 3.0 */
	*outbuf = alloc(RSA_size(pub->rsa));
	ret = RSA_public_encrypt((int)len, inbuf, *outbuf, pub->rsa,
		RSA_PKCS1_OAEP_PADDING);
	if (ret < 0) {
		free(*outbuf);
		*outbuf = NULL;
		return -E_ENCRYPT;
	}
	return ret;
#endif /* HAVE_OSSL_PARAM */
}

struct stream_cipher {
	EVP_CIPHER_CTX *aes;
};

struct stream_cipher *sc_new(const unsigned char *data, int len)
{
	struct stream_cipher *sc = alloc(sizeof(*sc));

	assert(len >= 2 * AES_CRT128_BLOCK_SIZE);
	assert((sc->aes = EVP_CIPHER_CTX_new()));
	EVP_EncryptInit_ex(sc->aes, EVP_aes_128_ctr(), NULL, data,
		data + AES_CRT128_BLOCK_SIZE);
	return sc;
}

void sc_free(struct stream_cipher *sc)
{
	if (!sc)
		return;
	EVP_CIPHER_CTX_free(sc->aes);
	free(sc);
}

static void aes_ctr128_crypt(EVP_CIPHER_CTX *ctx, struct iovec *src,
		struct iovec *dst)
{
	int ret, inlen = src->iov_len, outlen, tmplen;

	*dst = (typeof(*dst)) {
		/* Add one for the terminating zero byte. */
		.iov_base = alloc(inlen + 1),
		.iov_len = inlen
	};
	ret = EVP_EncryptUpdate(ctx, dst->iov_base, &outlen, src->iov_base, inlen);
	assert(ret != 0);
	ret = EVP_EncryptFinal_ex(ctx, dst->iov_base + outlen, &tmplen);
	assert(ret != 0);
	outlen += tmplen;
	((char *)dst->iov_base)[outlen] = '\0';
	dst->iov_len = outlen;
}

void sc_crypt(struct stream_cipher *sc, struct iovec *src, struct iovec *dst)
{
	return aes_ctr128_crypt(sc->aes, src, dst);
}

void hash_function(const char *data, unsigned long len, unsigned char *hash)
{
	int ret;
	EVP_MD_CTX *c;

	assert((c = EVP_MD_CTX_new()));
	ret = EVP_DigestInit_ex(c, EVP_sha256(), NULL);
	assert(ret != 0);
	ret = EVP_DigestUpdate(c, data, len);
	assert(ret != 0);
	ret = EVP_DigestFinal_ex(c, hash, NULL);
	assert(ret != 0);
	EVP_MD_CTX_free(c);
}