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| 1 | +/* |
| 2 | +Copyright IBM Corp. 2016 All Rights Reserved. |
| 3 | +
|
| 4 | +Licensed under the Apache License, Version 2.0 (the "License"); |
| 5 | +you may not use this file except in compliance with the License. |
| 6 | +You may obtain a copy of the License at |
| 7 | +
|
| 8 | + http://www.apache.org/licenses/LICENSE-2.0 |
| 9 | +
|
| 10 | +Unless required by applicable law or agreed to in writing, software |
| 11 | +distributed under the License is distributed on an "AS IS" BASIS, |
| 12 | +WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 13 | +See the License for the specific language governing permissions and |
| 14 | +limitations under the License. |
| 15 | +*/ |
| 16 | +/* |
| 17 | +Copyright IBM Corp. 2016 All Rights Reserved. |
| 18 | +
|
| 19 | +Licensed under the Apache License, Version 2.0 (the "License"); |
| 20 | +you may not use this file except in compliance with the License. |
| 21 | +You may obtain a copy of the License at |
| 22 | +
|
| 23 | + http://www.apache.org/licenses/LICENSE-2.0 |
| 24 | +
|
| 25 | +Unless required by applicable law or agreed to in writing, software |
| 26 | +distributed under the License is distributed on an "AS IS" BASIS, |
| 27 | +WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 28 | +See the License for the specific language governing permissions and |
| 29 | +limitations under the License. |
| 30 | +*/ |
| 31 | + |
| 32 | +package sw |
| 33 | + |
| 34 | +import ( |
| 35 | + "bytes" |
| 36 | + "crypto/aes" |
| 37 | + "crypto/cipher" |
| 38 | + "crypto/rand" |
| 39 | + "errors" |
| 40 | + "fmt" |
| 41 | + "io" |
| 42 | +) |
| 43 | + |
| 44 | +// GetRandomBytes returns len random looking bytes |
| 45 | +func GetRandomBytes(len int) ([]byte, error) { |
| 46 | + buffer := make([]byte, len) |
| 47 | + |
| 48 | + n, err := rand.Read(buffer) |
| 49 | + if err != nil { |
| 50 | + return nil, err |
| 51 | + } |
| 52 | + if n != len { |
| 53 | + return nil, fmt.Errorf("Buffer not filled. Requested [%d], got [%d]", len, n) |
| 54 | + } |
| 55 | + |
| 56 | + return buffer, nil |
| 57 | +} |
| 58 | + |
| 59 | +func pkcs7Padding(src []byte) []byte { |
| 60 | + padding := aes.BlockSize - len(src)%aes.BlockSize |
| 61 | + padtext := bytes.Repeat([]byte{byte(padding)}, padding) |
| 62 | + return append(src, padtext...) |
| 63 | +} |
| 64 | + |
| 65 | +func pkcs7UnPadding(src []byte) ([]byte, error) { |
| 66 | + length := len(src) |
| 67 | + unpadding := int(src[length-1]) |
| 68 | + |
| 69 | + if unpadding > aes.BlockSize || unpadding == 0 { |
| 70 | + return nil, errors.New("Invalid pkcs7 padding (unpadding > aes.BlockSize || unpadding == 0)") |
| 71 | + } |
| 72 | + |
| 73 | + pad := src[len(src)-unpadding:] |
| 74 | + for i := 0; i < unpadding; i++ { |
| 75 | + if pad[i] != byte(unpadding) { |
| 76 | + return nil, errors.New("Invalid pkcs7 padding (pad[i] != unpadding)") |
| 77 | + } |
| 78 | + } |
| 79 | + |
| 80 | + return src[:(length - unpadding)], nil |
| 81 | +} |
| 82 | + |
| 83 | +func aesCBCEncrypt(key, s []byte) ([]byte, error) { |
| 84 | + if len(s)%aes.BlockSize != 0 { |
| 85 | + return nil, errors.New("Invalid plaintext. It must be a multiple of the block size") |
| 86 | + } |
| 87 | + |
| 88 | + block, err := aes.NewCipher(key) |
| 89 | + if err != nil { |
| 90 | + return nil, err |
| 91 | + } |
| 92 | + |
| 93 | + ciphertext := make([]byte, aes.BlockSize+len(s)) |
| 94 | + iv := ciphertext[:aes.BlockSize] |
| 95 | + if _, err := io.ReadFull(rand.Reader, iv); err != nil { |
| 96 | + return nil, err |
| 97 | + } |
| 98 | + |
| 99 | + mode := cipher.NewCBCEncrypter(block, iv) |
| 100 | + mode.CryptBlocks(ciphertext[aes.BlockSize:], s) |
| 101 | + |
| 102 | + return ciphertext, nil |
| 103 | +} |
| 104 | + |
| 105 | +func aesCBCDecrypt(key, src []byte) ([]byte, error) { |
| 106 | + block, err := aes.NewCipher(key) |
| 107 | + if err != nil { |
| 108 | + return nil, err |
| 109 | + } |
| 110 | + |
| 111 | + if len(src) < aes.BlockSize { |
| 112 | + return nil, errors.New("Invalid ciphertext. It must be a multiple of the block size") |
| 113 | + } |
| 114 | + iv := src[:aes.BlockSize] |
| 115 | + src = src[aes.BlockSize:] |
| 116 | + |
| 117 | + if len(src)%aes.BlockSize != 0 { |
| 118 | + return nil, errors.New("Invalid ciphertext. It must be a multiple of the block size") |
| 119 | + } |
| 120 | + |
| 121 | + mode := cipher.NewCBCDecrypter(block, iv) |
| 122 | + |
| 123 | + mode.CryptBlocks(src, src) |
| 124 | + |
| 125 | + return src, nil |
| 126 | +} |
| 127 | + |
| 128 | +// AESCBCPKCS7Encrypt combines CBC encryption and PKCS7 padding |
| 129 | +func AESCBCPKCS7Encrypt(key, src []byte) ([]byte, error) { |
| 130 | + // First pad |
| 131 | + tmp := pkcs7Padding(src) |
| 132 | + |
| 133 | + // Then encrypt |
| 134 | + return aesCBCEncrypt(key, tmp) |
| 135 | +} |
| 136 | + |
| 137 | +// AESCBCPKCS7Decrypt combines CBC decryption and PKCS7 unpadding |
| 138 | +func AESCBCPKCS7Decrypt(key, src []byte) ([]byte, error) { |
| 139 | + // First decrypt |
| 140 | + pt, err := aesCBCDecrypt(key, src) |
| 141 | + if err != nil { |
| 142 | + return nil, err |
| 143 | + } |
| 144 | + |
| 145 | + // Then remove padding |
| 146 | + original, err := pkcs7UnPadding(pt) |
| 147 | + if err != nil { |
| 148 | + return nil, err |
| 149 | + } |
| 150 | + |
| 151 | + return original, nil |
| 152 | +} |
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