81 lines
2.7 KiB
Go
81 lines
2.7 KiB
Go
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// Package rfc4757 provides encryption and checksum methods as specified in RFC 4757
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package rfc4757
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import (
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"crypto/hmac"
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"crypto/rand"
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"crypto/rc4"
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"errors"
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"fmt"
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"gopkg.in/jcmturner/gokrb5.v7/crypto/etype"
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)
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// EncryptData encrypts the data provided using methods specific to the etype provided as defined in RFC 4757.
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func EncryptData(key, data []byte, e etype.EType) ([]byte, error) {
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if len(key) != e.GetKeyByteSize() {
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return []byte{}, fmt.Errorf("incorrect keysize: expected: %v actual: %v", e.GetKeyByteSize(), len(key))
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}
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rc4Cipher, err := rc4.NewCipher(key)
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if err != nil {
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return []byte{}, fmt.Errorf("error creating RC4 cipher: %v", err)
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}
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ed := make([]byte, len(data))
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copy(ed, data)
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rc4Cipher.XORKeyStream(ed, ed)
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rc4Cipher.Reset()
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return ed, nil
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}
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// DecryptData decrypts the data provided using the methods specific to the etype provided as defined in RFC 4757.
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func DecryptData(key, data []byte, e etype.EType) ([]byte, error) {
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return EncryptData(key, data, e)
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}
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// EncryptMessage encrypts the message provided using the methods specific to the etype provided as defined in RFC 4757.
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// The encrypted data is concatenated with its RC4 header containing integrity checksum and confounder to create an encrypted message.
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func EncryptMessage(key, data []byte, usage uint32, export bool, e etype.EType) ([]byte, error) {
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confounder := make([]byte, e.GetConfounderByteSize()) // size = 8
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_, err := rand.Read(confounder)
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if err != nil {
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return []byte{}, fmt.Errorf("error generating confounder: %v", err)
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}
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k1 := key
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k2 := HMAC(k1, UsageToMSMsgType(usage))
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toenc := append(confounder, data...)
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chksum := HMAC(k2, toenc)
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k3 := HMAC(k2, chksum)
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ed, err := EncryptData(k3, toenc, e)
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if err != nil {
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return []byte{}, fmt.Errorf("error encrypting data: %v", err)
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}
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msg := append(chksum, ed...)
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return msg, nil
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}
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// DecryptMessage decrypts the message provided using the methods specific to the etype provided as defined in RFC 4757.
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// The integrity of the message is also verified.
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func DecryptMessage(key, data []byte, usage uint32, export bool, e etype.EType) ([]byte, error) {
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checksum := data[:e.GetHMACBitLength()/8]
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ct := data[e.GetHMACBitLength()/8:]
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_, k2, k3 := deriveKeys(key, checksum, usage, export)
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pt, err := DecryptData(k3, ct, e)
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if err != nil {
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return []byte{}, fmt.Errorf("error decrypting data: %v", err)
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}
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if !VerifyIntegrity(k2, pt, data, e) {
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return []byte{}, errors.New("integrity checksum incorrect")
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}
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return pt[e.GetConfounderByteSize():], nil
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}
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// VerifyIntegrity checks the integrity checksum of the data matches that calculated from the decrypted data.
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func VerifyIntegrity(key, pt, data []byte, e etype.EType) bool {
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chksum := HMAC(key, pt)
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return hmac.Equal(chksum, data[:e.GetHMACBitLength()/8])
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}
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