Colin Cross | 7bb052a | 2015-02-03 12:59:37 -0800 | [diff] [blame^] | 1 | // Copyright 2012 The Go Authors. All rights reserved. |
| 2 | // Use of this source code is governed by a BSD-style |
| 3 | // license that can be found in the LICENSE file. |
| 4 | |
| 5 | package cipher_test |
| 6 | |
| 7 | import ( |
| 8 | "crypto/aes" |
| 9 | "crypto/cipher" |
| 10 | "crypto/rand" |
| 11 | "encoding/hex" |
| 12 | "fmt" |
| 13 | "io" |
| 14 | "os" |
| 15 | ) |
| 16 | |
| 17 | func ExampleNewCBCDecrypter() { |
| 18 | key := []byte("example key 1234") |
| 19 | ciphertext, _ := hex.DecodeString("f363f3ccdcb12bb883abf484ba77d9cd7d32b5baecb3d4b1b3e0e4beffdb3ded") |
| 20 | |
| 21 | block, err := aes.NewCipher(key) |
| 22 | if err != nil { |
| 23 | panic(err) |
| 24 | } |
| 25 | |
| 26 | // The IV needs to be unique, but not secure. Therefore it's common to |
| 27 | // include it at the beginning of the ciphertext. |
| 28 | if len(ciphertext) < aes.BlockSize { |
| 29 | panic("ciphertext too short") |
| 30 | } |
| 31 | iv := ciphertext[:aes.BlockSize] |
| 32 | ciphertext = ciphertext[aes.BlockSize:] |
| 33 | |
| 34 | // CBC mode always works in whole blocks. |
| 35 | if len(ciphertext)%aes.BlockSize != 0 { |
| 36 | panic("ciphertext is not a multiple of the block size") |
| 37 | } |
| 38 | |
| 39 | mode := cipher.NewCBCDecrypter(block, iv) |
| 40 | |
| 41 | // CryptBlocks can work in-place if the two arguments are the same. |
| 42 | mode.CryptBlocks(ciphertext, ciphertext) |
| 43 | |
| 44 | // If the original plaintext lengths are not a multiple of the block |
| 45 | // size, padding would have to be added when encrypting, which would be |
| 46 | // removed at this point. For an example, see |
| 47 | // https://tools.ietf.org/html/rfc5246#section-6.2.3.2. However, it's |
| 48 | // critical to note that ciphertexts must be authenticated (i.e. by |
| 49 | // using crypto/hmac) before being decrypted in order to avoid creating |
| 50 | // a padding oracle. |
| 51 | |
| 52 | fmt.Printf("%s\n", ciphertext) |
| 53 | // Output: exampleplaintext |
| 54 | } |
| 55 | |
| 56 | func ExampleNewCBCEncrypter() { |
| 57 | key := []byte("example key 1234") |
| 58 | plaintext := []byte("exampleplaintext") |
| 59 | |
| 60 | // CBC mode works on blocks so plaintexts may need to be padded to the |
| 61 | // next whole block. For an example of such padding, see |
| 62 | // https://tools.ietf.org/html/rfc5246#section-6.2.3.2. Here we'll |
| 63 | // assume that the plaintext is already of the correct length. |
| 64 | if len(plaintext)%aes.BlockSize != 0 { |
| 65 | panic("plaintext is not a multiple of the block size") |
| 66 | } |
| 67 | |
| 68 | block, err := aes.NewCipher(key) |
| 69 | if err != nil { |
| 70 | panic(err) |
| 71 | } |
| 72 | |
| 73 | // The IV needs to be unique, but not secure. Therefore it's common to |
| 74 | // include it at the beginning of the ciphertext. |
| 75 | ciphertext := make([]byte, aes.BlockSize+len(plaintext)) |
| 76 | iv := ciphertext[:aes.BlockSize] |
| 77 | if _, err := io.ReadFull(rand.Reader, iv); err != nil { |
| 78 | panic(err) |
| 79 | } |
| 80 | |
| 81 | mode := cipher.NewCBCEncrypter(block, iv) |
| 82 | mode.CryptBlocks(ciphertext[aes.BlockSize:], plaintext) |
| 83 | |
| 84 | // It's important to remember that ciphertexts must be authenticated |
| 85 | // (i.e. by using crypto/hmac) as well as being encrypted in order to |
| 86 | // be secure. |
| 87 | |
| 88 | fmt.Printf("%x\n", ciphertext) |
| 89 | } |
| 90 | |
| 91 | func ExampleNewCFBDecrypter() { |
| 92 | key := []byte("example key 1234") |
| 93 | ciphertext, _ := hex.DecodeString("22277966616d9bc47177bd02603d08c9a67d5380d0fe8cf3b44438dff7b9") |
| 94 | |
| 95 | block, err := aes.NewCipher(key) |
| 96 | if err != nil { |
| 97 | panic(err) |
| 98 | } |
| 99 | |
| 100 | // The IV needs to be unique, but not secure. Therefore it's common to |
| 101 | // include it at the beginning of the ciphertext. |
| 102 | if len(ciphertext) < aes.BlockSize { |
| 103 | panic("ciphertext too short") |
| 104 | } |
| 105 | iv := ciphertext[:aes.BlockSize] |
| 106 | ciphertext = ciphertext[aes.BlockSize:] |
| 107 | |
| 108 | stream := cipher.NewCFBDecrypter(block, iv) |
| 109 | |
| 110 | // XORKeyStream can work in-place if the two arguments are the same. |
| 111 | stream.XORKeyStream(ciphertext, ciphertext) |
| 112 | fmt.Printf("%s", ciphertext) |
| 113 | // Output: some plaintext |
| 114 | } |
| 115 | |
| 116 | func ExampleNewCFBEncrypter() { |
| 117 | key := []byte("example key 1234") |
| 118 | plaintext := []byte("some plaintext") |
| 119 | |
| 120 | block, err := aes.NewCipher(key) |
| 121 | if err != nil { |
| 122 | panic(err) |
| 123 | } |
| 124 | |
| 125 | // The IV needs to be unique, but not secure. Therefore it's common to |
| 126 | // include it at the beginning of the ciphertext. |
| 127 | ciphertext := make([]byte, aes.BlockSize+len(plaintext)) |
| 128 | iv := ciphertext[:aes.BlockSize] |
| 129 | if _, err := io.ReadFull(rand.Reader, iv); err != nil { |
| 130 | panic(err) |
| 131 | } |
| 132 | |
| 133 | stream := cipher.NewCFBEncrypter(block, iv) |
| 134 | stream.XORKeyStream(ciphertext[aes.BlockSize:], plaintext) |
| 135 | |
| 136 | // It's important to remember that ciphertexts must be authenticated |
| 137 | // (i.e. by using crypto/hmac) as well as being encrypted in order to |
| 138 | // be secure. |
| 139 | } |
| 140 | |
| 141 | func ExampleNewCTR() { |
| 142 | key := []byte("example key 1234") |
| 143 | plaintext := []byte("some plaintext") |
| 144 | |
| 145 | block, err := aes.NewCipher(key) |
| 146 | if err != nil { |
| 147 | panic(err) |
| 148 | } |
| 149 | |
| 150 | // The IV needs to be unique, but not secure. Therefore it's common to |
| 151 | // include it at the beginning of the ciphertext. |
| 152 | ciphertext := make([]byte, aes.BlockSize+len(plaintext)) |
| 153 | iv := ciphertext[:aes.BlockSize] |
| 154 | if _, err := io.ReadFull(rand.Reader, iv); err != nil { |
| 155 | panic(err) |
| 156 | } |
| 157 | |
| 158 | stream := cipher.NewCTR(block, iv) |
| 159 | stream.XORKeyStream(ciphertext[aes.BlockSize:], plaintext) |
| 160 | |
| 161 | // It's important to remember that ciphertexts must be authenticated |
| 162 | // (i.e. by using crypto/hmac) as well as being encrypted in order to |
| 163 | // be secure. |
| 164 | |
| 165 | // CTR mode is the same for both encryption and decryption, so we can |
| 166 | // also decrypt that ciphertext with NewCTR. |
| 167 | |
| 168 | plaintext2 := make([]byte, len(plaintext)) |
| 169 | stream = cipher.NewCTR(block, iv) |
| 170 | stream.XORKeyStream(plaintext2, ciphertext[aes.BlockSize:]) |
| 171 | |
| 172 | fmt.Printf("%s\n", plaintext2) |
| 173 | // Output: some plaintext |
| 174 | } |
| 175 | |
| 176 | func ExampleNewOFB() { |
| 177 | key := []byte("example key 1234") |
| 178 | plaintext := []byte("some plaintext") |
| 179 | |
| 180 | block, err := aes.NewCipher(key) |
| 181 | if err != nil { |
| 182 | panic(err) |
| 183 | } |
| 184 | |
| 185 | // The IV needs to be unique, but not secure. Therefore it's common to |
| 186 | // include it at the beginning of the ciphertext. |
| 187 | ciphertext := make([]byte, aes.BlockSize+len(plaintext)) |
| 188 | iv := ciphertext[:aes.BlockSize] |
| 189 | if _, err := io.ReadFull(rand.Reader, iv); err != nil { |
| 190 | panic(err) |
| 191 | } |
| 192 | |
| 193 | stream := cipher.NewOFB(block, iv) |
| 194 | stream.XORKeyStream(ciphertext[aes.BlockSize:], plaintext) |
| 195 | |
| 196 | // It's important to remember that ciphertexts must be authenticated |
| 197 | // (i.e. by using crypto/hmac) as well as being encrypted in order to |
| 198 | // be secure. |
| 199 | |
| 200 | // OFB mode is the same for both encryption and decryption, so we can |
| 201 | // also decrypt that ciphertext with NewOFB. |
| 202 | |
| 203 | plaintext2 := make([]byte, len(plaintext)) |
| 204 | stream = cipher.NewOFB(block, iv) |
| 205 | stream.XORKeyStream(plaintext2, ciphertext[aes.BlockSize:]) |
| 206 | |
| 207 | fmt.Printf("%s\n", plaintext2) |
| 208 | // Output: some plaintext |
| 209 | } |
| 210 | |
| 211 | func ExampleStreamReader() { |
| 212 | key := []byte("example key 1234") |
| 213 | |
| 214 | inFile, err := os.Open("encrypted-file") |
| 215 | if err != nil { |
| 216 | panic(err) |
| 217 | } |
| 218 | defer inFile.Close() |
| 219 | |
| 220 | block, err := aes.NewCipher(key) |
| 221 | if err != nil { |
| 222 | panic(err) |
| 223 | } |
| 224 | |
| 225 | // If the key is unique for each ciphertext, then it's ok to use a zero |
| 226 | // IV. |
| 227 | var iv [aes.BlockSize]byte |
| 228 | stream := cipher.NewOFB(block, iv[:]) |
| 229 | |
| 230 | outFile, err := os.OpenFile("decrypted-file", os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600) |
| 231 | if err != nil { |
| 232 | panic(err) |
| 233 | } |
| 234 | defer outFile.Close() |
| 235 | |
| 236 | reader := &cipher.StreamReader{S: stream, R: inFile} |
| 237 | // Copy the input file to the output file, decrypting as we go. |
| 238 | if _, err := io.Copy(outFile, reader); err != nil { |
| 239 | panic(err) |
| 240 | } |
| 241 | |
| 242 | // Note that this example is simplistic in that it omits any |
| 243 | // authentication of the encrypted data. If you were actually to use |
| 244 | // StreamReader in this manner, an attacker could flip arbitrary bits in |
| 245 | // the output. |
| 246 | } |
| 247 | |
| 248 | func ExampleStreamWriter() { |
| 249 | key := []byte("example key 1234") |
| 250 | |
| 251 | inFile, err := os.Open("plaintext-file") |
| 252 | if err != nil { |
| 253 | panic(err) |
| 254 | } |
| 255 | defer inFile.Close() |
| 256 | |
| 257 | block, err := aes.NewCipher(key) |
| 258 | if err != nil { |
| 259 | panic(err) |
| 260 | } |
| 261 | |
| 262 | // If the key is unique for each ciphertext, then it's ok to use a zero |
| 263 | // IV. |
| 264 | var iv [aes.BlockSize]byte |
| 265 | stream := cipher.NewOFB(block, iv[:]) |
| 266 | |
| 267 | outFile, err := os.OpenFile("encrypted-file", os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600) |
| 268 | if err != nil { |
| 269 | panic(err) |
| 270 | } |
| 271 | defer outFile.Close() |
| 272 | |
| 273 | writer := &cipher.StreamWriter{S: stream, W: outFile} |
| 274 | // Copy the input file to the output file, encrypting as we go. |
| 275 | if _, err := io.Copy(writer, inFile); err != nil { |
| 276 | panic(err) |
| 277 | } |
| 278 | |
| 279 | // Note that this example is simplistic in that it omits any |
| 280 | // authentication of the encrypted data. If you were actually to use |
| 281 | // StreamReader in this manner, an attacker could flip arbitrary bits in |
| 282 | // the decrypted result. |
| 283 | } |