src/crypto/x509/pem_decrypt.go - go - Git at Google

 // 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 if the PEM block is password encrypted.
 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 password encrypted PEM block 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 encrypted-PEM 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.
 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")
 	}

 	idx := strings.Index(dek, ",")
 	if idx == -1 {
 		return nil, errors.New("x509: malformed DEK-Info header")
 	}

 	mode, hexIV := dek[:idx], dek[idx+1:]
 	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.
 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
 }
	// 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 if the PEM block is password encrypted.
	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 password encrypted PEM block 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 encrypted-PEM 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.
	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")
	}

	idx := strings.Index(dek, ",")
	if idx == -1 {
	return nil, errors.New("x509: malformed DEK-Info header")
	}

	mode, hexIV := dek[:idx], dek[idx+1:]
	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.
	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
	}