vendor

vendor/github.com/google/certificate-transparency-go/x509/pem_decrypt.go

@@ -0,0 +1,240 @@
+// 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
+}