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// Copyright 2012 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package x509
// RFC 1423 describes the encryption of PEM blocks. The algorithm used to
// generate a key from the password was derived by looking at the OpenSSL
// implementation.
import (
"crypto/aes"
"crypto/cipher"
"crypto/des"
"crypto/md5"
"encoding/hex"
"encoding/pem"
"errors"
"io"
"strings"
)
type PEMCipher int
// Possible values for the EncryptPEMBlock encryption algorithm.
const (
_ PEMCipher = iota
PEMCipherDES
PEMCipher3DES
PEMCipherAES128
PEMCipherAES192
PEMCipherAES256
)
// rfc1423Algo holds a method for enciphering a PEM block.
type rfc1423Algo struct {
cipher PEMCipher
name string
cipherFunc func(key []byte) (cipher.Block, error)
keySize int
blockSize int
}
// rfc1423Algos holds a slice of the possible ways to encrypt a PEM
// block. The ivSize numbers were taken from the OpenSSL source.
var rfc1423Algos = []rfc1423Algo{{
cipher: PEMCipherDES,
name: "DES-CBC",
cipherFunc: des.NewCipher,
keySize: 8,
blockSize: des.BlockSize,
}, {
cipher: PEMCipher3DES,
name: "DES-EDE3-CBC",
cipherFunc: des.NewTripleDESCipher,
keySize: 24,
blockSize: des.BlockSize,
}, {
cipher: PEMCipherAES128,
name: "AES-128-CBC",
cipherFunc: aes.NewCipher,
keySize: 16,
blockSize: aes.BlockSize,
}, {
cipher: PEMCipherAES192,
name: "AES-192-CBC",
cipherFunc: aes.NewCipher,
keySize: 24,
blockSize: aes.BlockSize,
}, {
cipher: PEMCipherAES256,
name: "AES-256-CBC",
cipherFunc: aes.NewCipher,
keySize: 32,
blockSize: aes.BlockSize,
},
}
// deriveKey uses a key derivation function to stretch the password into a key
// with the number of bits our cipher requires. This algorithm was derived from
// the OpenSSL source.
func (c rfc1423Algo) deriveKey(password, salt []byte) []byte {
hash := md5.New()
out := make([]byte, c.keySize)
var digest []byte
for i := 0; i < len(out); i += len(digest) {
hash.Reset()
hash.Write(digest)
hash.Write(password)
hash.Write(salt)
digest = hash.Sum(digest[:0])
copy(out[i:], digest)
}
return out
}
// IsEncryptedPEMBlock returns whether the PEM block is password encrypted
// according to RFC 1423.
//
// Deprecated: Legacy PEM encryption as specified in RFC 1423 is insecure by
// design. Since it does not authenticate the ciphertext, it is vulnerable to
// padding oracle attacks that can let an attacker recover the plaintext.
func IsEncryptedPEMBlock(b *pem.Block) bool {
_, ok := b.Headers["DEK-Info"]
return ok
}
// IncorrectPasswordError is returned when an incorrect password is detected.
var IncorrectPasswordError = errors.New("x509: decryption password incorrect")
// DecryptPEMBlock takes a PEM block encrypted according to RFC 1423 and the
// password used to encrypt it and returns a slice of decrypted DER encoded
// bytes. It inspects the DEK-Info header to determine the algorithm used for
// decryption. If no DEK-Info header is present, an error is returned. If an
// incorrect password is detected an IncorrectPasswordError is returned. Because
// of deficiencies in the format, it's not always possible to detect an
// incorrect password. In these cases no error will be returned but the
// decrypted DER bytes will be random noise.
//
// Deprecated: Legacy PEM encryption as specified in RFC 1423 is insecure by
// design. Since it does not authenticate the ciphertext, it is vulnerable to
// padding oracle attacks that can let an attacker recover the plaintext.
func DecryptPEMBlock(b *pem.Block, password []byte) ([]byte, error) {
dek, ok := b.Headers["DEK-Info"]
if !ok {
return nil, errors.New("x509: no DEK-Info header in block")
}
mode, hexIV, ok := strings.Cut(dek, ",")
if !ok {
return nil, errors.New("x509: malformed DEK-Info header")
}
ciph := cipherByName(mode)
if ciph == nil {
return nil, errors.New("x509: unknown encryption mode")
}
iv, err := hex.DecodeString(hexIV)
if err != nil {
return nil, err
}
if len(iv) != ciph.blockSize {
return nil, errors.New("x509: incorrect IV size")
}
// Based on the OpenSSL implementation. The salt is the first 8 bytes
// of the initialization vector.
key := ciph.deriveKey(password, iv[:8])
block, err := ciph.cipherFunc(key)
if err != nil {
return nil, err
}
if len(b.Bytes)%block.BlockSize() != 0 {
return nil, errors.New("x509: encrypted PEM data is not a multiple of the block size")
}
data := make([]byte, len(b.Bytes))
dec := cipher.NewCBCDecrypter(block, iv)
dec.CryptBlocks(data, b.Bytes)
// Blocks are padded using a scheme where the last n bytes of padding are all
// equal to n. It can pad from 1 to blocksize bytes inclusive. See RFC 1423.
// For example:
// [x y z 2 2]
// [x y 7 7 7 7 7 7 7]
// If we detect a bad padding, we assume it is an invalid password.
dlen := len(data)
if dlen == 0 || dlen%ciph.blockSize != 0 {
return nil, errors.New("x509: invalid padding")
}
last := int(data[dlen-1])
if dlen < last {
return nil, IncorrectPasswordError
}
if last == 0 || last > ciph.blockSize {
return nil, IncorrectPasswordError
}
for _, val := range data[dlen-last:] {
if int(val) != last {
return nil, IncorrectPasswordError
}
}
return data[:dlen-last], nil
}
// EncryptPEMBlock returns a PEM block of the specified type holding the
// given DER encoded data encrypted with the specified algorithm and
// password according to RFC 1423.
//
// Deprecated: Legacy PEM encryption as specified in RFC 1423 is insecure by
// design. Since it does not authenticate the ciphertext, it is vulnerable to
// padding oracle attacks that can let an attacker recover the plaintext.
func EncryptPEMBlock(rand io.Reader, blockType string, data, password []byte, alg PEMCipher) (*pem.Block, error) {
ciph := cipherByKey(alg)
if ciph == nil {
return nil, errors.New("x509: unknown encryption mode")
}
iv := make([]byte, ciph.blockSize)
if _, err := io.ReadFull(rand, iv); err != nil {
return nil, errors.New("x509: cannot generate IV: " + err.Error())
}
// The salt is the first 8 bytes of the initialization vector,
// matching the key derivation in DecryptPEMBlock.
key := ciph.deriveKey(password, iv[:8])
block, err := ciph.cipherFunc(key)
if err != nil {
return nil, err
}
enc := cipher.NewCBCEncrypter(block, iv)
pad := ciph.blockSize - len(data)%ciph.blockSize
encrypted := make([]byte, len(data), len(data)+pad)
// We could save this copy by encrypting all the whole blocks in
// the data separately, but it doesn't seem worth the additional
// code.
copy(encrypted, data)
// See RFC 1423, Section 1.1.
for i := 0; i < pad; i++ {
encrypted = append(encrypted, byte(pad))
}
enc.CryptBlocks(encrypted, encrypted)
return &pem.Block{
Type: blockType,
Headers: map[string]string{
"Proc-Type": "4,ENCRYPTED",
"DEK-Info": ciph.name + "," + hex.EncodeToString(iv),
},
Bytes: encrypted,
}, nil
}
func cipherByName(name string) *rfc1423Algo {
for i := range rfc1423Algos {
alg := &rfc1423Algos[i]
if alg.name == name {
return alg
}
}
return nil
}
func cipherByKey(key PEMCipher) *rfc1423Algo {
for i := range rfc1423Algos {
alg := &rfc1423Algos[i]
if alg.cipher == key {
return alg
}
}
return nil
}
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