telebit/vendor/github.com/jcmturner/gokrb5/v8/crypto/rfc3961/encryption.go

120 lines
4.1 KiB
Go
Raw Normal View History

2020-06-03 06:18:04 +00:00
// Package rfc3961 provides encryption and checksum methods as specified in RFC 3961
package rfc3961
import (
"crypto/cipher"
"crypto/des"
"crypto/hmac"
"crypto/rand"
"errors"
"fmt"
"github.com/jcmturner/gokrb5/v8/crypto/common"
"github.com/jcmturner/gokrb5/v8/crypto/etype"
)
// DES3EncryptData encrypts the data provided using DES3 and methods specific to the etype provided.
func DES3EncryptData(key, data []byte, e etype.EType) ([]byte, []byte, error) {
if len(key) != e.GetKeyByteSize() {
return nil, nil, fmt.Errorf("incorrect keysize: expected: %v actual: %v", e.GetKeyByteSize(), len(key))
}
data, _ = common.ZeroPad(data, e.GetMessageBlockByteSize())
block, err := des.NewTripleDESCipher(key)
if err != nil {
return nil, nil, fmt.Errorf("error creating cipher: %v", err)
}
//RFC 3961: initial cipher state All bits zero
ivz := make([]byte, des.BlockSize)
ct := make([]byte, len(data))
mode := cipher.NewCBCEncrypter(block, ivz)
mode.CryptBlocks(ct, data)
return ct[len(ct)-e.GetMessageBlockByteSize():], ct, nil
}
// DES3EncryptMessage encrypts the message provided using DES3 and methods specific to the etype provided.
// The encrypted data is concatenated with its integrity hash to create an encrypted message.
func DES3EncryptMessage(key, message []byte, usage uint32, e etype.EType) ([]byte, []byte, error) {
//confounder
c := make([]byte, e.GetConfounderByteSize())
_, err := rand.Read(c)
if err != nil {
return []byte{}, []byte{}, fmt.Errorf("could not generate random confounder: %v", err)
}
plainBytes := append(c, message...)
plainBytes, _ = common.ZeroPad(plainBytes, e.GetMessageBlockByteSize())
// Derive key for encryption from usage
var k []byte
if usage != 0 {
k, err = e.DeriveKey(key, common.GetUsageKe(usage))
if err != nil {
return []byte{}, []byte{}, fmt.Errorf("error deriving key for encryption: %v", err)
}
}
iv, b, err := e.EncryptData(k, plainBytes)
if err != nil {
return iv, b, fmt.Errorf("error encrypting data: %v", err)
}
// Generate and append integrity hash
ih, err := common.GetIntegrityHash(plainBytes, key, usage, e)
if err != nil {
return iv, b, fmt.Errorf("error encrypting data: %v", err)
}
b = append(b, ih...)
return iv, b, nil
}
// DES3DecryptData decrypts the data provided using DES3 and methods specific to the etype provided.
func DES3DecryptData(key, data []byte, e etype.EType) ([]byte, error) {
if len(key) != e.GetKeyByteSize() {
return []byte{}, fmt.Errorf("incorrect keysize: expected: %v actual: %v", e.GetKeyByteSize(), len(key))
}
if len(data) < des.BlockSize || len(data)%des.BlockSize != 0 {
return []byte{}, errors.New("ciphertext is not a multiple of the block size")
}
block, err := des.NewTripleDESCipher(key)
if err != nil {
return []byte{}, fmt.Errorf("error creating cipher: %v", err)
}
pt := make([]byte, len(data))
ivz := make([]byte, des.BlockSize)
mode := cipher.NewCBCDecrypter(block, ivz)
mode.CryptBlocks(pt, data)
return pt, nil
}
// DES3DecryptMessage decrypts the message provided using DES3 and methods specific to the etype provided.
// The integrity of the message is also verified.
func DES3DecryptMessage(key, ciphertext []byte, usage uint32, e etype.EType) ([]byte, error) {
//Derive the key
k, err := e.DeriveKey(key, common.GetUsageKe(usage))
if err != nil {
return nil, fmt.Errorf("error deriving key: %v", err)
}
// Strip off the checksum from the end
b, err := e.DecryptData(k, ciphertext[:len(ciphertext)-e.GetHMACBitLength()/8])
if err != nil {
return nil, fmt.Errorf("error decrypting: %v", err)
}
//Verify checksum
if !e.VerifyIntegrity(key, ciphertext, b, usage) {
return nil, errors.New("error decrypting: integrity verification failed")
}
//Remove the confounder bytes
return b[e.GetConfounderByteSize():], nil
}
// VerifyIntegrity verifies the integrity of cipertext bytes ct.
func VerifyIntegrity(key, ct, pt []byte, usage uint32, etype etype.EType) bool {
h := make([]byte, etype.GetHMACBitLength()/8)
copy(h, ct[len(ct)-etype.GetHMACBitLength()/8:])
expectedMAC, _ := common.GetIntegrityHash(pt, key, usage, etype)
return hmac.Equal(h, expectedMAC)
}