/*
 * Copyright (C) 2009 Martin Willi
 * Copyright (C) 2002-2009 Andreas Steffen
 * Hochschule fuer Technik Rapperswil
 *
 * 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.  See <http://www.fsf.org/copyleft/gpl.txt>.
 *
 * 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.
 */

#include "pgp_builder.h"

#include <enum.h>
#include <debug.h>
#include <credentials/keys/private_key.h>

typedef enum pgp_pubkey_alg_t pgp_pubkey_alg_t;
typedef enum pgp_sym_alg_t pgp_sym_alg_t;

/**
 * OpenPGP public key algorithms as defined in section 9.1 of RFC 4880
 */
enum pgp_pubkey_alg_t {
	PGP_PUBKEY_ALG_RSA              =  1,
	PGP_PUBKEY_ALG_RSA_ENC_ONLY     =  2,
	PGP_PUBKEY_ALG_RSA_SIGN_ONLY    =  3,
	PGP_PUBKEY_ALG_ELGAMAL_ENC_ONLY = 16,
	PGP_PUBKEY_ALG_DSA              = 17,
	PGP_PUBKEY_ALG_ECC              = 18,
	PGP_PUBKEY_ALG_ECDSA            = 19,
	PGP_PUBKEY_ALG_ELGAMAL          = 20,
	PGP_PUBKEY_ALG_DIFFIE_HELLMAN   = 21,
};

/**
 * OpenPGP symmetric key algorithms as defined in section 9.2 of RFC 4880
 */
enum pgp_sym_alg_t {
	PGP_SYM_ALG_PLAIN    =  0,
	PGP_SYM_ALG_IDEA     =  1,
	PGP_SYM_ALG_3DES     =  2,
	PGP_SYM_ALG_CAST5    =  3,
	PGP_SYM_ALG_BLOWFISH =  4,
	PGP_SYM_ALG_SAFER    =  5,
	PGP_SYM_ALG_DES      =  6,
	PGP_SYM_ALG_AES_128  =  7,
	PGP_SYM_ALG_AES_192  =  8,
	PGP_SYM_ALG_AES_256  =  9,
	PGP_SYM_ALG_TWOFISH  = 10
};

ENUM_BEGIN(pgp_pubkey_alg_names, PGP_PUBKEY_ALG_RSA, PGP_PUBKEY_ALG_RSA_SIGN_ONLY,
	"RSA",
	"RSA_ENC_ONLY",
	"RSA_SIGN_ONLY"
);
ENUM_NEXT(pgp_pubkey_alg_names, PGP_PUBKEY_ALG_ELGAMAL_ENC_ONLY, PGP_PUBKEY_ALG_DIFFIE_HELLMAN, PGP_PUBKEY_ALG_RSA_SIGN_ONLY,
	"ELGAMAL_ENC_ONLY",
	"DSA",
	"ECC",
	"ECDSA",
	"ELGAMAL",
	"DIFFIE_HELLMAN"
);
ENUM_END(pgp_pubkey_alg_names, PGP_PUBKEY_ALG_DIFFIE_HELLMAN);

ENUM(pgp_sym_alg_names, PGP_SYM_ALG_PLAIN, PGP_SYM_ALG_TWOFISH,
	"PLAINTEXT",
	"IDEA",
	"3DES",
	"CAST5",
	"BLOWFISH",
	"SAFER",
	"DES",
	"AES_128",
	"AES_192",
	"AES_256",
	"TWOFISH"
);

/**
 * Read a PGP scalar of bytes length, advance blob
 */
static bool read_scalar(chunk_t *blob, size_t bytes, u_int32_t *scalar)
{
	u_int32_t res = 0;

	if (bytes > blob->len)
	{
		DBG1("PGP data too short to read %d byte scalar", bytes);
		return FALSE;
	}
	while (bytes-- > 0)
	{
		res = 256 * res + blob->ptr[0];
		*blob = chunk_skip(*blob, 1);
	}
	*scalar = res;
	return TRUE;
}

/**
 * Read length of an PGP old packet length encoding
 */
static bool old_packet_length(chunk_t *blob, u_int32_t *length)
{
	/* bits 0 and 1 define the packet length type */
	u_char type;

	if (!blob->len)
	{
		return FALSE;
	}
	type = 0x03 & blob->ptr[0];
	*blob = chunk_skip(*blob, 1);

	if (type > 2)
	{
		return FALSE;
	}
	return read_scalar(blob, type == 0 ? 1 : type * 2, length);
}

/**
 * Read a PGP MPI, advance blob
 */
static bool read_mpi(chunk_t *blob, chunk_t *mpi)
{
	u_int32_t bits, bytes;

	if (!read_scalar(blob, 2, &bits))
	{
		DBG1("PGP data too short to read MPI length");
		return FALSE;
	}
	bytes = (bits + 7) / 8;
	if (bytes > blob->len)
	{
		DBG1("PGP data too short to read %d byte MPI", bytes);
		return FALSE;
	}
	*mpi = chunk_create(blob->ptr, bytes);
	*blob = chunk_skip(*blob, bytes);
	return TRUE;
}

/**
 * Load a generic public key from a PGP packet
 */
static public_key_t *parse_public_key(chunk_t blob)
{
	u_int32_t alg;
	public_key_t *key;

	if (!read_scalar(&blob, 1, &alg))
	{
		return NULL;
	}
	switch (alg)
	{
		case PGP_PUBKEY_ALG_RSA:
		case PGP_PUBKEY_ALG_RSA_SIGN_ONLY:
			key = lib->creds->create(lib->creds, CRED_PUBLIC_KEY, KEY_RSA,
									 BUILD_BLOB_PGP, blob, BUILD_END);
			break;
		default:
			DBG1("PGP public key algorithm %N not supported",
				 pgp_pubkey_alg_names, alg);
			return NULL;
	}
	return key;
}

/**
 * Load a RSA public key from a PGP packet
 */
static public_key_t *parse_rsa_public_key(chunk_t blob)
{
	chunk_t mpi[2];
	int i;

	for (i = 0; i < 2; i++)
	{
		if (!read_mpi(&blob, &mpi[i]))
		{
			return NULL;
		}
	}
	return lib->creds->create(lib->creds, CRED_PUBLIC_KEY, KEY_RSA,
						BUILD_RSA_MODULUS, mpi[0], BUILD_RSA_PUB_EXP, mpi[1],
						BUILD_END);
}

/**
 * Load a RSA private key from a PGP packet
 */
static private_key_t *parse_rsa_private_key(chunk_t blob)
{
	chunk_t mpi[6];
	u_int32_t s2k;
	int i;

	for (i = 0; i < 2; i++)
	{
		if (!read_mpi(&blob, &mpi[i]))
		{
			return NULL;
		}
	}
	if (!read_scalar(&blob, 1, &s2k))
	{
		return NULL;
	}
	if (s2k == 255 || s2k == 254)
	{
		DBG1("string-to-key specifiers not supported");
		return NULL;
	}
	if (s2k != PGP_SYM_ALG_PLAIN)
	{
		DBG1("%N private key encryption not supported", pgp_sym_alg_names, s2k);
		return NULL;
	}

	for (i = 2; i < 6; i++)
	{
		if (!read_mpi(&blob, &mpi[i]))
		{
			return NULL;
		}
	}

	/* PGP has uses p < q, but we use p > q */
	return lib->creds->create(lib->creds, CRED_PRIVATE_KEY, KEY_RSA,
						BUILD_RSA_MODULUS, mpi[0], BUILD_RSA_PUB_EXP, mpi[1],
						BUILD_RSA_PRIV_EXP, mpi[2], BUILD_RSA_PRIME2, mpi[3],
						BUILD_RSA_PRIME1, mpi[4], BUILD_RSA_COEFF, mpi[5],
						BUILD_END);
}

/**
 * Implementation of private_key_t.sign for encryption-only keys
 */
static bool sign_not_allowed(private_key_t *this, signature_scheme_t scheme,
							 chunk_t data, chunk_t *signature)
{
	DBG1("signing failed - decryption only key");
	return FALSE;
}

/**
 * Implementation of private_key_t.decrypt for signature-only keys
 */
static bool decrypt_not_allowed(private_key_t *this,
								chunk_t crypto, chunk_t *plain)
{
	DBG1("decryption failed - signature only key");
	return FALSE;
}

/**
 * Load a generic private key from a PGP packet
 */
static private_key_t *parse_private_key(chunk_t blob)
{
	chunk_t packet;
	u_char tag, type;
	u_int32_t len, version, created, days, alg;
	private_key_t *key;

	tag = blob.ptr[0];

	/* bit 7 must be set */
	if (!(tag & 0x80))
	{
		DBG1("invalid packet tag");
		return NULL;
	}
	/* bit 6 set defines new packet format */
	if (tag & 0x40)
	{
		DBG1("new PGP packet format not supported");
		return NULL;
	}

	type = (tag & 0x3C) >> 2;
	if (!old_packet_length(&blob, &len) || len > blob.len)
	{
		DBG1("invalid packet length");
		return NULL;
	}
	packet.len = len;
	packet.ptr = blob.ptr;
	blob = chunk_skip(blob, len);

	if (!read_scalar(&packet, 1, &version))
	{
		return NULL;
	}
	if (version < 3 || version > 4)
	{
		DBG1("OpenPGP packet version V%d not supported", version);
		return NULL;
	}
	if (!read_scalar(&packet, 4, &created))
	{
		return NULL;
	}
	if (version == 3)
	{
		if (!read_scalar(&packet, 2, &days))
		{
			return NULL;
		}
	}
	if (!read_scalar(&packet, 1, &alg))
	{
		return NULL;
	}
	switch (alg)
	{
		case PGP_PUBKEY_ALG_RSA:
			return lib->creds->create(lib->creds, CRED_PRIVATE_KEY, KEY_RSA,
									  BUILD_BLOB_PGP, packet, BUILD_END);
		case PGP_PUBKEY_ALG_RSA_ENC_ONLY:
			key = lib->creds->create(lib->creds, CRED_PRIVATE_KEY, KEY_RSA,
									  BUILD_BLOB_PGP, packet, BUILD_END);
			if (key)
			{
				key->sign = sign_not_allowed;
			}
			return key;
		case PGP_PUBKEY_ALG_RSA_SIGN_ONLY:
			key = lib->creds->create(lib->creds, CRED_PRIVATE_KEY, KEY_RSA,
									  BUILD_BLOB_PGP, packet, BUILD_END);
			if (key)
			{
				key->decrypt = decrypt_not_allowed;
			}
			return key;
		case PGP_PUBKEY_ALG_ECDSA:
			return lib->creds->create(lib->creds, CRED_PRIVATE_KEY, KEY_ECDSA,
									  BUILD_BLOB_PGP, packet, BUILD_END);
		case PGP_PUBKEY_ALG_ELGAMAL_ENC_ONLY:
		case PGP_PUBKEY_ALG_DSA:
		case PGP_PUBKEY_ALG_ECC:
		case PGP_PUBKEY_ALG_ELGAMAL:
		case PGP_PUBKEY_ALG_DIFFIE_HELLMAN:
		default:
			return NULL;
	}
}

/**
 *  See header.
 */
public_key_t *pgp_public_key_load(key_type_t type, va_list args)
{
	chunk_t blob = chunk_empty;

	while (TRUE)
	{
		switch (va_arg(args, builder_part_t))
		{
			case BUILD_BLOB_PGP:
				blob = va_arg(args, chunk_t);
				continue;
			case BUILD_END:
				break;
			default:
				return NULL;
		}
		break;
	}
	switch (type)
	{
		case KEY_ANY:
			return parse_public_key(blob);
		case KEY_RSA:
			return parse_rsa_public_key(blob);
		default:
			return NULL;
	}
}

/**
 * See header.
 */
private_key_t *pgp_private_key_load(key_type_t type, va_list args)
{
	chunk_t blob = chunk_empty;

	while (TRUE)
	{
		switch (va_arg(args, builder_part_t))
		{
			case BUILD_BLOB_PGP:
				blob = va_arg(args, chunk_t);
				continue;
			case BUILD_END:
				break;
			default:
				return NULL;
		}
		break;
	}
	switch (type)
	{
		case KEY_ANY:
			return parse_private_key(blob);
		case KEY_RSA:
			return parse_rsa_private_key(blob);
		default:
			return NULL;
	}
}