Package cipher implements standard block cipher modes that can be wrapped around low-level block cipher implementations. See http://csrc.nist.gov/groups/ST/toolkit/BCM/current_modes.html and NIST Special Publication 800-38A.
cbc.go cfb.go cipher.go ctr.go gcm.go io.go ofb.go xor.go
AEAD is a cipher mode providing authenticated encryption with associated data. For a description of the methodology, see
https://en.wikipedia.org/wiki/Authenticated_encryption
type AEAD interface {
// NonceSize returns the size of the nonce that must be passed to Seal
// and Open.
NonceSize() int
// Overhead returns the maximum difference between the lengths of a
// plaintext and its ciphertext.
Overhead() int
// Seal encrypts and authenticates plaintext, authenticates the
// additional data and appends the result to dst, returning the updated
// slice. The nonce must be NonceSize() bytes long and unique for all
// time, for a given key.
//
// The plaintext and dst may alias exactly or not at all. To reuse
// plaintext's storage for the encrypted output, use plaintext[:0] as dst.
Seal(dst, nonce, plaintext, additionalData []byte) []byte
// Open decrypts and authenticates ciphertext, authenticates the
// additional data and, if successful, appends the resulting plaintext
// to dst, returning the updated slice. The nonce must be NonceSize()
// bytes long and both it and the additional data must match the
// value passed to Seal.
//
// The ciphertext and dst may alias exactly or not at all. To reuse
// ciphertext's storage for the decrypted output, use ciphertext[:0] as dst.
//
// Even if the function fails, the contents of dst, up to its capacity,
// may be overwritten.
Open(dst, nonce, ciphertext, additionalData []byte) ([]byte, error)
} func NewGCM(cipher Block) (AEAD, error)
NewGCM returns the given 128-bit, block cipher wrapped in Galois Counter Mode with the standard nonce length.
In general, the GHASH operation performed by this implementation of GCM is not constant-time. An exception is when the underlying Block was created by aes.NewCipher on systems with hardware support for AES. See the crypto/aes package documentation for details.
package main
import (
"crypto/aes"
"crypto/cipher"
"encoding/hex"
"fmt"
)
func main() {
// The key argument should be the AES key, either 16 or 32 bytes
// to select AES-128 or AES-256.
key := []byte("AES256Key-32Characters1234567890")
ciphertext, _ := hex.DecodeString("1019aa66cd7c024f9efd0038899dae1973ee69427f5a6579eba292ffe1b5a260")
nonce, _ := hex.DecodeString("37b8e8a308c354048d245f6d")
block, err := aes.NewCipher(key)
if err != nil {
panic(err.Error())
}
aesgcm, err := cipher.NewGCM(block)
if err != nil {
panic(err.Error())
}
plaintext, err := aesgcm.Open(nil, nonce, ciphertext, nil)
if err != nil {
panic(err.Error())
}
fmt.Printf("%s\n", plaintext)
}
package main
import (
"crypto/aes"
"crypto/cipher"
"crypto/rand"
"fmt"
"io"
)
func main() {
// The key argument should be the AES key, either 16 or 32 bytes
// to select AES-128 or AES-256.
key := []byte("AES256Key-32Characters1234567890")
plaintext := []byte("exampleplaintext")
block, err := aes.NewCipher(key)
if err != nil {
panic(err.Error())
}
// Never use more than 2^32 random nonces with a given key because of the risk of a repeat.
nonce := make([]byte, 12)
if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
panic(err.Error())
}
aesgcm, err := cipher.NewGCM(block)
if err != nil {
panic(err.Error())
}
ciphertext := aesgcm.Seal(nil, nonce, plaintext, nil)
fmt.Printf("%x\n", ciphertext)
}
func NewGCMWithNonceSize(cipher Block, size int) (AEAD, error)
NewGCMWithNonceSize returns the given 128-bit, block cipher wrapped in Galois Counter Mode, which accepts nonces of the given length.
Only use this function if you require compatibility with an existing cryptosystem that uses non-standard nonce lengths. All other users should use NewGCM, which is faster and more resistant to misuse.
A Block represents an implementation of block cipher using a given key. It provides the capability to encrypt or decrypt individual blocks. The mode implementations extend that capability to streams of blocks.
type Block interface {
// BlockSize returns the cipher's block size.
BlockSize() int
// Encrypt encrypts the first block in src into dst.
// Dst and src may point at the same memory.
Encrypt(dst, src []byte)
// Decrypt decrypts the first block in src into dst.
// Dst and src may point at the same memory.
Decrypt(dst, src []byte)
} A BlockMode represents a block cipher running in a block-based mode (CBC, ECB etc).
type BlockMode interface {
// BlockSize returns the mode's block size.
BlockSize() int
// CryptBlocks encrypts or decrypts a number of blocks. The length of
// src must be a multiple of the block size. Dst and src may point to
// the same memory.
CryptBlocks(dst, src []byte)
} func NewCBCDecrypter(b Block, iv []byte) BlockMode
NewCBCDecrypter returns a BlockMode which decrypts in cipher block chaining mode, using the given Block. The length of iv must be the same as the Block's block size and must match the iv used to encrypt the data.
package main
import (
"crypto/aes"
"crypto/cipher"
"encoding/hex"
"fmt"
)
func main() {
key := []byte("example key 1234")
ciphertext, _ := hex.DecodeString("f363f3ccdcb12bb883abf484ba77d9cd7d32b5baecb3d4b1b3e0e4beffdb3ded")
block, err := aes.NewCipher(key)
if err != nil {
panic(err)
}
// The IV needs to be unique, but not secure. Therefore it's common to
// include it at the beginning of the ciphertext.
if len(ciphertext) < aes.BlockSize {
panic("ciphertext too short")
}
iv := ciphertext[:aes.BlockSize]
ciphertext = ciphertext[aes.BlockSize:]
// CBC mode always works in whole blocks.
if len(ciphertext)%aes.BlockSize != 0 {
panic("ciphertext is not a multiple of the block size")
}
mode := cipher.NewCBCDecrypter(block, iv)
// CryptBlocks can work in-place if the two arguments are the same.
mode.CryptBlocks(ciphertext, ciphertext)
// If the original plaintext lengths are not a multiple of the block
// size, padding would have to be added when encrypting, which would be
// removed at this point. For an example, see
// https://tools.ietf.org/html/rfc5246#section-6.2.3.2. However, it's
// critical to note that ciphertexts must be authenticated (i.e. by
// using crypto/hmac) before being decrypted in order to avoid creating
// a padding oracle.
fmt.Printf("%s\n", ciphertext)
}
func NewCBCEncrypter(b Block, iv []byte) BlockMode
NewCBCEncrypter returns a BlockMode which encrypts in cipher block chaining mode, using the given Block. The length of iv must be the same as the Block's block size.
package main
import (
"crypto/aes"
"crypto/cipher"
"crypto/rand"
"fmt"
"io"
)
func main() {
key := []byte("example key 1234")
plaintext := []byte("exampleplaintext")
// CBC mode works on blocks so plaintexts may need to be padded to the
// next whole block. For an example of such padding, see
// https://tools.ietf.org/html/rfc5246#section-6.2.3.2. Here we'll
// assume that the plaintext is already of the correct length.
if len(plaintext)%aes.BlockSize != 0 {
panic("plaintext is not a multiple of the block size")
}
block, err := aes.NewCipher(key)
if err != nil {
panic(err)
}
// The IV needs to be unique, but not secure. Therefore it's common to
// include it at the beginning of the ciphertext.
ciphertext := make([]byte, aes.BlockSize+len(plaintext))
iv := ciphertext[:aes.BlockSize]
if _, err := io.ReadFull(rand.Reader, iv); err != nil {
panic(err)
}
mode := cipher.NewCBCEncrypter(block, iv)
mode.CryptBlocks(ciphertext[aes.BlockSize:], plaintext)
// It's important to remember that ciphertexts must be authenticated
// (i.e. by using crypto/hmac) as well as being encrypted in order to
// be secure.
fmt.Printf("%x\n", ciphertext)
}
A Stream represents a stream cipher.
type Stream interface {
// XORKeyStream XORs each byte in the given slice with a byte from the
// cipher's key stream. Dst and src may point to the same memory.
// If len(dst) < len(src), XORKeyStream should panic. It is acceptable
// to pass a dst bigger than src, and in that case, XORKeyStream will
// only update dst[:len(src)] and will not touch the rest of dst.
XORKeyStream(dst, src []byte)
} func NewCFBDecrypter(block Block, iv []byte) Stream
NewCFBDecrypter returns a Stream which decrypts with cipher feedback mode, using the given Block. The iv must be the same length as the Block's block size.
package main
import (
"crypto/aes"
"crypto/cipher"
"encoding/hex"
"fmt"
)
func main() {
key := []byte("example key 1234")
ciphertext, _ := hex.DecodeString("22277966616d9bc47177bd02603d08c9a67d5380d0fe8cf3b44438dff7b9")
block, err := aes.NewCipher(key)
if err != nil {
panic(err)
}
// The IV needs to be unique, but not secure. Therefore it's common to
// include it at the beginning of the ciphertext.
if len(ciphertext) < aes.BlockSize {
panic("ciphertext too short")
}
iv := ciphertext[:aes.BlockSize]
ciphertext = ciphertext[aes.BlockSize:]
stream := cipher.NewCFBDecrypter(block, iv)
// XORKeyStream can work in-place if the two arguments are the same.
stream.XORKeyStream(ciphertext, ciphertext)
fmt.Printf("%s", ciphertext)
}
func NewCFBEncrypter(block Block, iv []byte) Stream
NewCFBEncrypter returns a Stream which encrypts with cipher feedback mode, using the given Block. The iv must be the same length as the Block's block size.
package main
import (
"crypto/aes"
"crypto/cipher"
"crypto/rand"
"io"
)
func main() {
key := []byte("example key 1234")
plaintext := []byte("some plaintext")
block, err := aes.NewCipher(key)
if err != nil {
panic(err)
}
// The IV needs to be unique, but not secure. Therefore it's common to
// include it at the beginning of the ciphertext.
ciphertext := make([]byte, aes.BlockSize+len(plaintext))
iv := ciphertext[:aes.BlockSize]
if _, err := io.ReadFull(rand.Reader, iv); err != nil {
panic(err)
}
stream := cipher.NewCFBEncrypter(block, iv)
stream.XORKeyStream(ciphertext[aes.BlockSize:], plaintext)
// It's important to remember that ciphertexts must be authenticated
// (i.e. by using crypto/hmac) as well as being encrypted in order to
// be secure.
}
func NewCTR(block Block, iv []byte) Stream
NewCTR returns a Stream which encrypts/decrypts using the given Block in counter mode. The length of iv must be the same as the Block's block size.
package main
import (
"crypto/aes"
"crypto/cipher"
"crypto/rand"
"fmt"
"io"
)
func main() {
key := []byte("example key 1234")
plaintext := []byte("some plaintext")
block, err := aes.NewCipher(key)
if err != nil {
panic(err)
}
// The IV needs to be unique, but not secure. Therefore it's common to
// include it at the beginning of the ciphertext.
ciphertext := make([]byte, aes.BlockSize+len(plaintext))
iv := ciphertext[:aes.BlockSize]
if _, err := io.ReadFull(rand.Reader, iv); err != nil {
panic(err)
}
stream := cipher.NewCTR(block, iv)
stream.XORKeyStream(ciphertext[aes.BlockSize:], plaintext)
// It's important to remember that ciphertexts must be authenticated
// (i.e. by using crypto/hmac) as well as being encrypted in order to
// be secure.
// CTR mode is the same for both encryption and decryption, so we can
// also decrypt that ciphertext with NewCTR.
plaintext2 := make([]byte, len(plaintext))
stream = cipher.NewCTR(block, iv)
stream.XORKeyStream(plaintext2, ciphertext[aes.BlockSize:])
fmt.Printf("%s\n", plaintext2)
}
func NewOFB(b Block, iv []byte) Stream
NewOFB returns a Stream that encrypts or decrypts using the block cipher b in output feedback mode. The initialization vector iv's length must be equal to b's block size.
package main
import (
"crypto/aes"
"crypto/cipher"
"crypto/rand"
"fmt"
"io"
)
func main() {
key := []byte("example key 1234")
plaintext := []byte("some plaintext")
block, err := aes.NewCipher(key)
if err != nil {
panic(err)
}
// The IV needs to be unique, but not secure. Therefore it's common to
// include it at the beginning of the ciphertext.
ciphertext := make([]byte, aes.BlockSize+len(plaintext))
iv := ciphertext[:aes.BlockSize]
if _, err := io.ReadFull(rand.Reader, iv); err != nil {
panic(err)
}
stream := cipher.NewOFB(block, iv)
stream.XORKeyStream(ciphertext[aes.BlockSize:], plaintext)
// It's important to remember that ciphertexts must be authenticated
// (i.e. by using crypto/hmac) as well as being encrypted in order to
// be secure.
// OFB mode is the same for both encryption and decryption, so we can
// also decrypt that ciphertext with NewOFB.
plaintext2 := make([]byte, len(plaintext))
stream = cipher.NewOFB(block, iv)
stream.XORKeyStream(plaintext2, ciphertext[aes.BlockSize:])
fmt.Printf("%s\n", plaintext2)
}
StreamReader wraps a Stream into an io.Reader. It calls XORKeyStream to process each slice of data which passes through.
type StreamReader struct {
S Stream
R io.Reader
} package main
import (
"crypto/aes"
"crypto/cipher"
"io"
"os"
)
func main() {
key := []byte("example key 1234")
inFile, err := os.Open("encrypted-file")
if err != nil {
panic(err)
}
defer inFile.Close()
block, err := aes.NewCipher(key)
if err != nil {
panic(err)
}
// If the key is unique for each ciphertext, then it's ok to use a zero
// IV.
var iv [aes.BlockSize]byte
stream := cipher.NewOFB(block, iv[:])
outFile, err := os.OpenFile("decrypted-file", os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
if err != nil {
panic(err)
}
defer outFile.Close()
reader := &cipher.StreamReader{S: stream, R: inFile}
// Copy the input file to the output file, decrypting as we go.
if _, err := io.Copy(outFile, reader); err != nil {
panic(err)
}
// Note that this example is simplistic in that it omits any
// authentication of the encrypted data. If you were actually to use
// StreamReader in this manner, an attacker could flip arbitrary bits in
// the output.
}
func (r StreamReader) Read(dst []byte) (n int, err error)
StreamWriter wraps a Stream into an io.Writer. It calls XORKeyStream to process each slice of data which passes through. If any Write call returns short then the StreamWriter is out of sync and must be discarded. A StreamWriter has no internal buffering; Close does not need to be called to flush write data.
type StreamWriter struct {
S Stream
W io.Writer
Err error // unused
} package main
import (
"crypto/aes"
"crypto/cipher"
"io"
"os"
)
func main() {
key := []byte("example key 1234")
inFile, err := os.Open("plaintext-file")
if err != nil {
panic(err)
}
defer inFile.Close()
block, err := aes.NewCipher(key)
if err != nil {
panic(err)
}
// If the key is unique for each ciphertext, then it's ok to use a zero
// IV.
var iv [aes.BlockSize]byte
stream := cipher.NewOFB(block, iv[:])
outFile, err := os.OpenFile("encrypted-file", os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
if err != nil {
panic(err)
}
defer outFile.Close()
writer := &cipher.StreamWriter{S: stream, W: outFile}
// Copy the input file to the output file, encrypting as we go.
if _, err := io.Copy(writer, inFile); err != nil {
panic(err)
}
// Note that this example is simplistic in that it omits any
// authentication of the encrypted data. If you were actually to use
// StreamReader in this manner, an attacker could flip arbitrary bits in
// the decrypted result.
}
func (w StreamWriter) Close() error
Close closes the underlying Writer and returns its Close return value, if the Writer is also an io.Closer. Otherwise it returns nil.
func (w StreamWriter) Write(src []byte) (n int, err error)
© Google, Inc.
Licensed under the Creative Commons Attribution License 3.0.
https://golang.org/pkg/crypto/cipher/