package crypto

import (
	"crypto/aes"
	"crypto/hmac"
	"crypto/sha1"
	"hash"

	"gopkg.in/jcmturner/gokrb5.v7/crypto/common"
	"gopkg.in/jcmturner/gokrb5.v7/crypto/rfc3961"
	"gopkg.in/jcmturner/gokrb5.v7/crypto/rfc3962"
	"gopkg.in/jcmturner/gokrb5.v7/iana/chksumtype"
	"gopkg.in/jcmturner/gokrb5.v7/iana/etypeID"
)

// RFC 3962
//+--------------------------------------------------------------------+
//|               protocol key format        128- or 256-bit string    |
//|                                                                    |
//|            string-to-key function        PBKDF2+DK with variable   |
//|                                          iteration count (see      |
//|                                          above)                    |
//|                                                                    |
//|  default string-to-key parameters        00 00 10 00               |
//|                                                                    |
//|        key-generation seed length        key size                  |
//|                                                                    |
//|            random-to-key function        identity function         |
//|                                                                    |
//|                  hash function, H        SHA-1                     |
//|                                                                    |
//|               HMAC output size, h        12 octets (96 bits)       |
//|                                                                    |
//|             message block size, m        1 octet                   |
//|                                                                    |
//|  encryption/decryption functions,        AES in CBC-CTS mode       |
//|  E and D                                 (cipher block size 16     |
//|                                          octets), with next-to-    |
//|                                          last block (last block    |
//|                                          if only one) as CBC-style |
//|                                          ivec                      |
//+--------------------------------------------------------------------+
//
//+--------------------------------------------------------------------+
//|                         encryption types                           |
//+--------------------------------------------------------------------+
//|         type name                  etype value          key size   |
//+--------------------------------------------------------------------+
//|   aes128-cts-hmac-sha1-96              17                 128      |
//|   aes256-cts-hmac-sha1-96              18                 256      |
//+--------------------------------------------------------------------+
//
//+--------------------------------------------------------------------+
//|                          checksum types                            |
//+--------------------------------------------------------------------+
//|        type name                 sumtype value           length    |
//+--------------------------------------------------------------------+
//|    hmac-sha1-96-aes128                15                   96      |
//|    hmac-sha1-96-aes256                16                   96      |
//+--------------------------------------------------------------------+

// Aes256CtsHmacSha96 implements Kerberos encryption type aes256-cts-hmac-sha1-96
type Aes256CtsHmacSha96 struct {
}

// GetETypeID returns the EType ID number.
func (e Aes256CtsHmacSha96) GetETypeID() int32 {
	return etypeID.AES256_CTS_HMAC_SHA1_96
}

// GetHashID returns the checksum type ID number.
func (e Aes256CtsHmacSha96) GetHashID() int32 {
	return chksumtype.HMAC_SHA1_96_AES256
}

// GetKeyByteSize returns the number of bytes for key of this etype.
func (e Aes256CtsHmacSha96) GetKeyByteSize() int {
	return 256 / 8
}

// GetKeySeedBitLength returns the number of bits for the seed for key generation.
func (e Aes256CtsHmacSha96) GetKeySeedBitLength() int {
	return e.GetKeyByteSize() * 8
}

// GetHashFunc returns the hash function for this etype.
func (e Aes256CtsHmacSha96) GetHashFunc() func() hash.Hash {
	return sha1.New
}

// GetMessageBlockByteSize returns the block size for the etype's messages.
func (e Aes256CtsHmacSha96) GetMessageBlockByteSize() int {
	return 1
}

// GetDefaultStringToKeyParams returns the default key derivation parameters in string form.
func (e Aes256CtsHmacSha96) GetDefaultStringToKeyParams() string {
	return "00001000"
}

// GetConfounderByteSize returns the byte count for confounder to be used during cryptographic operations.
func (e Aes256CtsHmacSha96) GetConfounderByteSize() int {
	return aes.BlockSize
}

// GetHMACBitLength returns the bit count size of the integrity hash.
func (e Aes256CtsHmacSha96) GetHMACBitLength() int {
	return 96
}

// GetCypherBlockBitLength returns the bit count size of the cypher block.
func (e Aes256CtsHmacSha96) GetCypherBlockBitLength() int {
	return aes.BlockSize * 8
}

// StringToKey returns a key derived from the string provided.
func (e Aes256CtsHmacSha96) StringToKey(secret string, salt string, s2kparams string) ([]byte, error) {
	return rfc3962.StringToKey(secret, salt, s2kparams, e)
}

// RandomToKey returns a key from the bytes provided.
func (e Aes256CtsHmacSha96) RandomToKey(b []byte) []byte {
	return rfc3961.RandomToKey(b)
}

// EncryptData encrypts the data provided.
func (e Aes256CtsHmacSha96) EncryptData(key, data []byte) ([]byte, []byte, error) {
	return rfc3962.EncryptData(key, data, e)
}

// EncryptMessage encrypts the message provided and concatenates it with the integrity hash to create an encrypted message.
func (e Aes256CtsHmacSha96) EncryptMessage(key, message []byte, usage uint32) ([]byte, []byte, error) {
	return rfc3962.EncryptMessage(key, message, usage, e)
}

// DecryptData decrypts the data provided.
func (e Aes256CtsHmacSha96) DecryptData(key, data []byte) ([]byte, error) {
	return rfc3962.DecryptData(key, data, e)
}

// DecryptMessage decrypts the message provided and verifies the integrity of the message.
func (e Aes256CtsHmacSha96) DecryptMessage(key, ciphertext []byte, usage uint32) ([]byte, error) {
	return rfc3962.DecryptMessage(key, ciphertext, usage, e)
}

// DeriveKey derives a key from the protocol key based on the usage value.
func (e Aes256CtsHmacSha96) DeriveKey(protocolKey, usage []byte) ([]byte, error) {
	return rfc3961.DeriveKey(protocolKey, usage, e)
}

// DeriveRandom generates data needed for key generation.
func (e Aes256CtsHmacSha96) DeriveRandom(protocolKey, usage []byte) ([]byte, error) {
	return rfc3961.DeriveRandom(protocolKey, usage, e)
}

// VerifyIntegrity checks the integrity of the plaintext message.
func (e Aes256CtsHmacSha96) VerifyIntegrity(protocolKey, ct, pt []byte, usage uint32) bool {
	return rfc3961.VerifyIntegrity(protocolKey, ct, pt, usage, e)
}

// GetChecksumHash returns a keyed checksum hash of the bytes provided.
func (e Aes256CtsHmacSha96) GetChecksumHash(protocolKey, data []byte, usage uint32) ([]byte, error) {
	return common.GetHash(data, protocolKey, common.GetUsageKc(usage), e)
}

// VerifyChecksum compares the checksum of the message bytes is the same as the checksum provided.
func (e Aes256CtsHmacSha96) VerifyChecksum(protocolKey, data, chksum []byte, usage uint32) bool {
	c, err := e.GetChecksumHash(protocolKey, data, usage)
	if err != nil {
		return false
	}
	return hmac.Equal(chksum, c)
}