/*
 * decrypt.c - Part of the Linux-NTFS project.
 *
 * Copyright (c) 2005 Yuval Fledel
 *
 * $EFS decryption routines.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program (in the main directory of the Linux-NTFS distribution
 * in the file COPYING); if not, write to the Free Software Foundation,
 * Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include "config.h"

#include <stdio.h>
#include <errno.h>
#include <gcrypt.h>
#include <openssl/md5.h>

#include "decrypt.h"

#ifdef __CYGWIN__
//#define USE_CRYPTOAPI_RSA 1
#define _WIN32_WINNT 0x501
#define WINVER 0x501

#include <windows.h>
#include <wincrypt.h>

/* Missing cygwin macros */
#ifndef CERT_SYSTEM_STORE_CURRENT_USER
#define CERT_SYSTEM_STORE_CURRENT_USER 0x00010000
#endif

#ifndef CERT_CLOSE_STORE_CHECK_FLAG
#define CERT_CLOSE_STORE_CHECK_FLAG 2
#endif

#ifndef CRYPT_ACQUIRE_CACHE_FLAG
#define CRYPT_ACQUIRE_CACHE_FLAG 1
#endif

/* windows 2k+ imports */
typedef BOOL (WINAPI *LPFN_CryptAcquireCertificatePrivateKey) (PCCERT_CONTEXT,
		DWORD, void *, HCRYPTPROV *, DWORD *, BOOL*);
typedef BOOL (WINAPI *LPFN_CertCloseStore) (HCERTSTORE, DWORD);
typedef PCCERT_CONTEXT (WINAPI *LPFN_CertFindCertificateInStore) (HCERTSTORE, 
		DWORD, DWORD, DWORD, const void*, PCCERT_CONTEXT);
typedef BOOL (WINAPI *LPFN_CertFreeCertificateContext) (PCCERT_CONTEXT);
typedef HCERTSTORE (WINAPI *LPFN_CertOpenStore) (LPCSTR, DWORD, HCRYPTPROV, 
		DWORD, const void*);

// NT4SP3+ WINME or 95+ w/ IE5+
static LPFN_CryptAcquireCertificatePrivateKey 
	fnCryptAcquireCertificatePrivateKey; 
// osr2+ NT4SP3+ or NT4 w/ IE3.02:
static LPFN_CertCloseStore fnCertCloseStore;
static LPFN_CertFindCertificateInStore fnCertFindCertificateInStore;
static LPFN_CertFreeCertificateContext fnCertFreeCertificateContext;
static LPFN_CertOpenStore fnCertOpenStore;

/* global variable: handle to crypt32.dll */
static HMODULE hCrypt32 = INVALID_HANDLE_VALUE;

#else /* defined(__CYGWIN__) */

#include <malloc.h>
#include <string.h>
/* If not one of the below three, use standard Des. */
#define CALG_3DES (0x6603)
#define CALG_DESX (0x6604)
#define CALG_AES_256 (0x6610)

#endif /* defined(__CYGWIN__) */

/* This must be after windows.h include. */
#include "types.h"

typedef struct {
#ifdef __CYGWIN__
	HCERTSTORE hSystemStore;
#else
	int nothing; /* unused */
#endif /* defined(__CYGWIN__) */
} DECRYPT_SESSION;

typedef struct {
	u64 desx_key[3];
	u8 *key_data;
	u32 alg_id;
	gcry_cipher_hd_t gcry_cipher_hd; // handle to the decrypted FEK.
	gcry_sexp_t sexp_key;  // the user's RSA key.
#ifdef USE_CRYPTOAPI_RSA
	HCRYPTKEY hCryptKey;
#endif /* defined(__CYGWIN__) */
} DECRYPT_KEY;

#ifdef __CYGWIN__

static int cryptoAPI_init_imports(void)
{
	if (hCrypt32 == INVALID_HANDLE_VALUE)
		hCrypt32 = LoadLibrary("crypt32.dll");

	if (!fnCryptAcquireCertificatePrivateKey)
		fnCryptAcquireCertificatePrivateKey = 
			(LPFN_CryptAcquireCertificatePrivateKey)
			GetProcAddress(hCrypt32,
			"CryptAcquireCertificatePrivateKey");
	if (!fnCertCloseStore)
		fnCertCloseStore = (LPFN_CertCloseStore)
			GetProcAddress(hCrypt32, "CertCloseStore");
	if (!fnCertFindCertificateInStore)
		fnCertFindCertificateInStore = 
			(LPFN_CertFindCertificateInStore)
			GetProcAddress(hCrypt32, "CertFindCertificateInStore");
	if (!fnCertFreeCertificateContext)
		fnCertFreeCertificateContext = 
			(LPFN_CertFreeCertificateContext)
			GetProcAddress(hCrypt32, "CertFreeCertificateContext");
	if (!fnCertOpenStore)
		fnCertOpenStore = (LPFN_CertOpenStore)
			GetProcAddress(hCrypt32, "CertOpenStore");

	return fnCryptAcquireCertificatePrivateKey && fnCertCloseStore &&
		fnCertFindCertificateInStore &&
		fnCertFreeCertificateContext && fnCertOpenStore;
}
#endif /* defined(__CYGWIN__) */

decrypt_session *decrypt_open(void) {
	decrypt_session *session;

	gcry_control(GCRYCTL_DISABLE_SECMEM, 0);

#ifdef __CYGWIN__
	HCERTSTORE hSystemStore;

	if (!cryptoAPI_init_imports()) {
		fprintf(stderr, "Some imports do not exist.\n");
		errno = -1;
		return NULL;
	}

	if (!(hSystemStore = fnCertOpenStore(((LPCSTR)CERT_STORE_PROV_SYSTEM),
			0, (HCRYPTPROV)NULL, CERT_SYSTEM_STORE_CURRENT_USER,
			L"MY"))) {
		fprintf(stderr, "Could not open system store.\n");
		errno = -1;
		return NULL;
	}
#endif /* defined(__CYGWIN__) */

	session = (decrypt_session *)malloc(sizeof(DECRYPT_SESSION));
#ifdef __CYGWIN__
	((DECRYPT_SESSION *)session)->hSystemStore = hSystemStore;
#endif /* defined(__CYGWIN__) */
	return session;
}

void decrypt_close(decrypt_session *session) {
#ifdef __CYGWIN__
	if (((DECRYPT_SESSION *)session)->hSystemStore)
		fnCertCloseStore(((DECRYPT_SESSION *)session)->hSystemStore,
					CERT_CLOSE_STORE_CHECK_FLAG);
	/* fixme: racy */
	FreeLibrary(hCrypt32);
	hCrypt32 = INVALID_HANDLE_VALUE;
#endif /* defined(__CYGWIN__) */

	free(session);
}

static inline void reverse_buffer(unsigned char *buf, unsigned int buf_size) {
    unsigned char t;
    unsigned int i;

    for (i=0; i<buf_size/2; i++) {
        t = buf[i];
        buf[i] = buf[buf_size-i-1];
        buf[buf_size-i-1] = t;
    }
}

decrypt_key *decrypt_user_key_open(decrypt_session *session
			__attribute__((unused)),
			int thumb_size, void *thumb_print) {
#ifdef __CYGWIN__
	CRYPT_HASH_BLOB hash_blob;
	HCRYPTPROV hCryptProv;
	PCCERT_CONTEXT pCert;
	BOOL fCallerFreeProv;
	HCRYPTKEY hCryptKey;
	decrypt_key *key;
	DWORD dwKeySpec;
	DWORD key_size;
	BYTE key_blob[1000];

	hash_blob.cbData = thumb_size;
	hash_blob.pbData = thumb_print;

	if (!(pCert = fnCertFindCertificateInStore(
				((DECRYPT_SESSION *)session)->hSystemStore,
				(PKCS_7_ASN_ENCODING | X509_ASN_ENCODING),
				0, CERT_FIND_HASH, &hash_blob, NULL))) {
		fprintf(stderr, "Could not find cert in store.\n");
		goto decrypt_key_open_err;
	}

	dwKeySpec = AT_KEYEXCHANGE;
	if (!fnCryptAcquireCertificatePrivateKey(pCert,
				CRYPT_ACQUIRE_CACHE_FLAG, NULL,
				&hCryptProv, &dwKeySpec,
				&fCallerFreeProv)) {
		fprintf(stderr, "Could not aquire private key from cert.\n");
		goto decrypt_key_open_err;
	}

	if (!CryptGetUserKey(hCryptProv, AT_KEYEXCHANGE, &hCryptKey)) {
		fprintf(stderr, "Could not aquire user key.\n");
		goto decrypt_key_open_err;
	}

	key_size = sizeof(key_blob);
	if (!CryptExportKey(hCryptKey, 0, PRIVATEKEYBLOB, 0, key_blob, &key_size)) {
		fprintf(stderr, "Could not export key: Error 0x%x\n",
					(unsigned int)GetLastError());
		errno = -1;
		return NULL;
	}

	if (!(key = (decrypt_key *)malloc(sizeof(DECRYPT_KEY))))
		goto decrypt_key_open_err;

#ifdef USE_CRYPTOAPI_RSA
	((DECRYPT_KEY *)key)->hCryptKey = hCryptKey;
#else
	RSAPUBKEY *rsa_pub_key = (RSAPUBKEY *)(key_blob + sizeof(PUBLICKEYSTRUC));
	gcry_ac_handle_t gcry_handle;
	unsigned char *mpi_data;
	gcry_mpi_t n,e,d,p,q,u;
	gcry_sexp_t sexp_key;
	gcry_error_t err;
	size_t size;
	int rc;

	CryptDestroyKey(hCryptKey);

	if ((err = gcry_ac_open(&gcry_handle, GCRY_AC_RSA, 0))) {
		fprintf(stderr, "Could not init gcrypt handle\n");
		errno = -1;
		return NULL;
	}

	e = gcry_mpi_set_ui(NULL, rsa_pub_key->pubexp);

	mpi_data = (key_blob + 0x14);
	size = rsa_pub_key->bitlen / 8;
	reverse_buffer(mpi_data, size);
	if ((rc = gcry_mpi_scan(&n, GCRYMPI_FMT_USG, mpi_data, size, &size))) {
		fprintf(stderr, "error scanning n.\n");
	}

	mpi_data += (rsa_pub_key->bitlen / 8);
	size = rsa_pub_key->bitlen / 16;
	reverse_buffer(mpi_data, size);
	if ((rc = gcry_mpi_scan(&q, GCRYMPI_FMT_USG, mpi_data, size, &size))) {
		fprintf(stderr, "error scanning p.\n");
	}

	mpi_data += (rsa_pub_key->bitlen / 16);
	size = rsa_pub_key->bitlen / 16;
	reverse_buffer(mpi_data, size);
	if ((rc = gcry_mpi_scan(&p, GCRYMPI_FMT_USG, mpi_data, size, &size))) {
		fprintf(stderr, "error scanning q.\n");
	}

	mpi_data += (rsa_pub_key->bitlen / 16)*3;
	size = rsa_pub_key->bitlen / 16;
	reverse_buffer(mpi_data, size);
	if ((rc = gcry_mpi_scan(&u, GCRYMPI_FMT_USG, mpi_data, size, &size))) {
		fprintf(stderr, "error scanning u.\n");
	}

	mpi_data += (rsa_pub_key->bitlen / 16);
	size = rsa_pub_key->bitlen / 8;
	reverse_buffer(mpi_data, size);
	if ((rc = gcry_mpi_scan(&d, GCRYMPI_FMT_USG, mpi_data, size, &size))) {
		fprintf(stderr, "error scanning d.\n");
	}

	if ((rc = gcry_sexp_build(&sexp_key, NULL,
			"(private-key (rsa (n %m) (e %m) (d %m) (p %m) (q %m) (u %m)))",
			n, e, d, p, q, u))) {
		fprintf(stderr, "Could build sexp from data, (error = 0x%x)\n", rc);
		errno = -1;
		return FALSE;
	}

	((DECRYPT_KEY *)key)->sexp_key = sexp_key;

	// todo: release all
#endif
	return key;

decrypt_key_open_err:

	if (hCryptKey)
		CryptDestroyKey(hCryptKey);
	if (pCert)
		fnCertFreeCertificateContext(pCert);
#endif // defined(__CYGWIN__)
	errno = ENOTSUP;
	return NULL;
}

void decrypt_user_key_close(decrypt_key *key) {
	DECRYPT_KEY *dkey = (DECRYPT_KEY *)key;
	if (dkey->gcry_cipher_hd)
		gcry_cipher_close(dkey->gcry_cipher_hd);

	free(key);
}

/**
 * decrypt_decrypt
 *
 * warning: decrypting into the input buffer!
 */
unsigned int decrypt_decrypt(decrypt_key *key, unsigned int data_size, 
					unsigned char *data)
{
#ifdef USE_CRYPTOAPI_RSA
	DWORD size = data_size;

	if (!CryptDecrypt(((DECRYPT_KEY *)key)->hCryptKey, 0, 
				TRUE, 0, data, &size)) {
		errno = -1;
		return 0;
	}

	return size;
#else
	gcry_sexp_t sexp_plain_data, sexp_enc_data;
	gcry_ac_handle_t gcry_handle;
	gcry_mpi_t mpi_buf;
	gcry_ac_data_t in;
	gcry_error_t err;
	unsigned int size, padding_length, i;
	int rc;

	if ((err = gcry_ac_open(&gcry_handle, GCRY_AC_RSA, 0))) {
		fprintf(stderr, "Could not init gcrypt handle\n");
		errno = -1;
		return FALSE;
	}

	if ((rc = gcry_ac_data_new(&in))) {
		fprintf(stderr, "error allocating 'in'.\n");
	}

	reverse_buffer(data, data_size);

	size = data_size;
	if ((rc = gcry_mpi_scan(&mpi_buf, GCRYMPI_FMT_USG, data, (size_t)data_size, &size))) {
		fprintf(stderr, "error scanning 'in'.\n");
	}

	if ((rc = gcry_sexp_build(&sexp_enc_data, &size, "(enc-val (flags) (rsa (a %m)))", mpi_buf))) {
		fprintf(stderr, "Could build sexp from data, (error = 0x%x)\n", rc);
		errno = -1;
		return FALSE;
	}

	if ((rc = gcry_pk_decrypt(&sexp_plain_data, sexp_enc_data, ((DECRYPT_KEY *)key)->sexp_key))) {
		fprintf(stderr, "Could not decrypt fek via s-exp, (error = 0x%x)\n", rc);
		errno = -1;
		return FALSE;
	}

	sexp_plain_data = gcry_sexp_find_token(sexp_plain_data, "value", 0);
	if (!mpi_buf) {
		fprintf(stderr, "Could find value in s-exp, (error = 0x%x)\n", rc);
		errno = -1;
		return FALSE;
	}

	mpi_buf = gcry_sexp_nth_mpi(sexp_plain_data, 1, GCRYMPI_FMT_USG);

	if ((rc = gcry_mpi_print(GCRYMPI_FMT_USG, data, data_size, &size, mpi_buf))) {
		fprintf(stderr, "Could copy decrypted data back, (error = 0x%x)\n", rc);
		errno = -1;
		return FALSE;
	}

	// remove the pkcs1 padding
	for (padding_length = 1;(padding_length<size) && data[padding_length];
		padding_length++);
	padding_length++;
	for (i = 0;i+padding_length<size;i++) // todo: should memcpy fit? (overlapping)
		data[i]=data[padding_length+i];

	// todo: mpi_buf->data
	// todo: release all
	gcry_ac_data_destroy(in);

	return size - padding_length;
#endif // USER_CRYPTOAPI_RSA (else)
}

unsigned int decrypt_decrypt_sector(decrypt_key *key, void *data,
			unsigned long long offset) {
	gcry_error_t gcry_error2;
	DECRYPT_KEY *dkey = (DECRYPT_KEY *)key;

	// FIXME: Why are we not calling gcry_cipher_setiv() here instead of
	// doing it by hand after the decryption?

	if (dkey->alg_id != CALG_DESX) {
		if ((gcry_error2 = gcry_cipher_reset(dkey->gcry_cipher_hd)))
			fprintf(stderr, "gcry_error2 is %u.\n", gcry_error2);
		if ((gcry_error2 = gcry_cipher_decrypt(dkey->gcry_cipher_hd,
				data, 512, NULL, 0)))
			fprintf(stderr, "gcry_error2 is %u.\n", gcry_error2);
	} else {
		u64 *pos;

		/* Set @pos to last eight bytes of sector @data. */
		pos = (u64*)(data + 512 - 8);
		do {
			if ((gcry_error2 = gcry_cipher_reset(
					dkey->gcry_cipher_hd)))
				fprintf(stderr, "gcry_error2 is %u.\n",
						gcry_error2);
			/* Apply in-whitening. */
			*pos ^= dkey->desx_key[0];
			/* Apply DES decyption. */
			if ((gcry_error2 = gcry_cipher_decrypt(
					dkey->gcry_cipher_hd, (u8*)pos, 8,
					NULL, 0)))
				fprintf(stderr, "gcry_error2 is %u.\n",
						gcry_error2);
			/* Apply out-whitening. */
			*pos ^= dkey->desx_key[1];
			if (pos == (u64*)data)
				break;
			*pos ^= *(pos - 1);
			pos--;
		} while (1);
	}
	/* Apply the IV. */
	if (dkey->alg_id == CALG_AES_256) {
		((u64*)data)[0] ^= 0x5816657be9161312LL + offset;
		((u64*)data)[1] ^= 0x1989adbe44918961LL + offset;
	} else {
		/* All other algos (Des, 3Des, DesX) use the same IV. */
		((u64*)data)[0] ^= 0x169119629891ad13LL + offset;
	}
	return 512;
}

/**
 * desx_key_expand - expand a 128-bit desx key to the needed 192-bit key
 * @src:	source buffer containing 128-bit key
 * @dst:	destination buffer to write 192-bit key to
 *
 * Expands the on-disk 128-bit desx key to the needed full 192-bit desx key
 * required to perform desx {de,en}cryption.
 *
 * FIXME: Is this endianness safe?  I think so but I may be wrong...
 */
static void desx_key_expand(u8 *src, u8* dst) {
	static const int salt_len = 12;
	static const u8 *salt1 = "Dan Simon  ";
	static const u8 *salt2 = "Scott Field";
	u8 md[16];
	MD5_CTX ctx1, ctx2;

	MD5_Init(&ctx1);

	/* Hash the on-disk key. */
	MD5_Update(&ctx1, src, 128 / 8);
	memcpy(&ctx2, &ctx1, sizeof(ctx1));

	/* Hash with the first salt and store the result. */
	MD5_Update(&ctx1, salt1, salt_len);
	MD5_Final(md, &ctx1);
	((u32*)dst)[0] = ((u32*)md)[0] ^ ((u32*)md)[1];
	((u32*)dst)[1] = ((u32*)md)[2] ^ ((u32*)md)[3];

	/* Hash with the second salt and store the result. */
	MD5_Update(&ctx2, salt2, salt_len);
	MD5_Final(md, &ctx2);
	memcpy(dst + 8, md, sizeof(md));

	return;
}

decrypt_key *decrypt_make_key(decrypt_session *session __attribute__((unused)), 
		unsigned int data_size __attribute__((unused)),
		unsigned char *data) {
	DECRYPT_KEY *key;
	unsigned int key_size, gcry_algo;
	int gcry_length, gcry_mode;
	gcry_error_t gcry_error2;

	key_size = *(u32*)data;

	if (!(key = (DECRYPT_KEY *)malloc(sizeof(DECRYPT_KEY)))) {
		errno = -1;
		return NULL;
	}

	key->alg_id = *(u32*)(data + 8);
	key->key_data = data + 16;
	gcry_mode = GCRY_CIPHER_MODE_CBC;

	switch (key->alg_id) {
	case CALG_DESX:
		fprintf(stderr, "DESX key of %u bytes\n", key_size);
		fprintf(stderr, "on-disk key (hex) = 0x%llx, 0x%llx\n",
				*(u64*)key->key_data, *(u64*)(key->key_data+8));
		desx_key_expand(key->key_data, (u8*)&key->desx_key);
		fprintf(stderr, "expanded keys (hex) = 0x%llx, 0x%llx, "
				"0x%llx\n", key->desx_key[0], key->desx_key[1],
				key->desx_key[2]);
		key->key_data = (u8*)&key->desx_key[2];
		gcry_mode = GCRY_CIPHER_MODE_ECB;
		gcry_length = 8;
		gcry_algo = GCRY_CIPHER_DES;
		break;
	case CALG_3DES:
		fprintf(stderr, "3DES Key of %u bytes\n", key_size);
		gcry_length = 24;
		gcry_algo = GCRY_CIPHER_3DES; 
		break;
	case CALG_AES_256:
		fprintf(stderr, "AES Key of %u bytes\n", key_size);
		gcry_length = 32;
		gcry_algo = GCRY_CIPHER_AES256;
		break;
	default:
		fprintf(stderr, "DES key of %u bytes\n", key_size);
		gcry_length = 8;
		gcry_algo = GCRY_CIPHER_DES;
		break;
	}
	if ((gcry_error2 = gcry_cipher_open(&key->gcry_cipher_hd,
			gcry_algo, gcry_mode, 0)) != GPG_ERR_NO_ERROR) {
		fprintf(stderr, "gcry_error1 is %u.\n", gcry_error2);
		errno = -1;
		return 0;
	}
	if ((gcry_error2 = gcry_cipher_setkey(key->gcry_cipher_hd,
			key->key_data, gcry_length))) {
		fprintf(stderr, "gcry_error2 is %u.\n", gcry_error2);
	}
	return (decrypt_key *)key;
}