Brent Austin | ba3052e | 2015-04-21 16:08:23 -0700 | [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 x509 |
| 6 | |
| 7 | // RFC 1423 describes the encryption of PEM blocks. The algorithm used to |
| 8 | // generate a key from the password was derived by looking at the OpenSSL |
| 9 | // implementation. |
| 10 | |
| 11 | import ( |
| 12 | "crypto/aes" |
| 13 | "crypto/cipher" |
| 14 | "crypto/des" |
| 15 | "crypto/md5" |
| 16 | "encoding/hex" |
| 17 | "encoding/pem" |
| 18 | "errors" |
| 19 | "io" |
| 20 | "strings" |
| 21 | ) |
| 22 | |
| 23 | type PEMCipher int |
| 24 | |
| 25 | // Possible values for the EncryptPEMBlock encryption algorithm. |
| 26 | const ( |
| 27 | _ PEMCipher = iota |
| 28 | PEMCipherDES |
| 29 | PEMCipher3DES |
| 30 | PEMCipherAES128 |
| 31 | PEMCipherAES192 |
| 32 | PEMCipherAES256 |
| 33 | ) |
| 34 | |
| 35 | // rfc1423Algo holds a method for enciphering a PEM block. |
| 36 | type rfc1423Algo struct { |
| 37 | cipher PEMCipher |
| 38 | name string |
| 39 | cipherFunc func(key []byte) (cipher.Block, error) |
| 40 | keySize int |
| 41 | blockSize int |
| 42 | } |
| 43 | |
| 44 | // rfc1423Algos holds a slice of the possible ways to encrypt a PEM |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 45 | // block. The ivSize numbers were taken from the OpenSSL source. |
Brent Austin | ba3052e | 2015-04-21 16:08:23 -0700 | [diff] [blame] | 46 | var rfc1423Algos = []rfc1423Algo{{ |
| 47 | cipher: PEMCipherDES, |
| 48 | name: "DES-CBC", |
| 49 | cipherFunc: des.NewCipher, |
| 50 | keySize: 8, |
| 51 | blockSize: des.BlockSize, |
| 52 | }, { |
| 53 | cipher: PEMCipher3DES, |
| 54 | name: "DES-EDE3-CBC", |
| 55 | cipherFunc: des.NewTripleDESCipher, |
| 56 | keySize: 24, |
| 57 | blockSize: des.BlockSize, |
| 58 | }, { |
| 59 | cipher: PEMCipherAES128, |
| 60 | name: "AES-128-CBC", |
| 61 | cipherFunc: aes.NewCipher, |
| 62 | keySize: 16, |
| 63 | blockSize: aes.BlockSize, |
| 64 | }, { |
| 65 | cipher: PEMCipherAES192, |
| 66 | name: "AES-192-CBC", |
| 67 | cipherFunc: aes.NewCipher, |
| 68 | keySize: 24, |
| 69 | blockSize: aes.BlockSize, |
| 70 | }, { |
| 71 | cipher: PEMCipherAES256, |
| 72 | name: "AES-256-CBC", |
| 73 | cipherFunc: aes.NewCipher, |
| 74 | keySize: 32, |
| 75 | blockSize: aes.BlockSize, |
| 76 | }, |
| 77 | } |
| 78 | |
| 79 | // deriveKey uses a key derivation function to stretch the password into a key |
| 80 | // with the number of bits our cipher requires. This algorithm was derived from |
| 81 | // the OpenSSL source. |
| 82 | func (c rfc1423Algo) deriveKey(password, salt []byte) []byte { |
| 83 | hash := md5.New() |
| 84 | out := make([]byte, c.keySize) |
| 85 | var digest []byte |
| 86 | |
| 87 | for i := 0; i < len(out); i += len(digest) { |
| 88 | hash.Reset() |
| 89 | hash.Write(digest) |
| 90 | hash.Write(password) |
| 91 | hash.Write(salt) |
| 92 | digest = hash.Sum(digest[:0]) |
| 93 | copy(out[i:], digest) |
| 94 | } |
| 95 | return out |
| 96 | } |
| 97 | |
Colin Cross | 1f80552 | 2021-05-14 11:10:59 -0700 | [diff] [blame] | 98 | // IsEncryptedPEMBlock returns whether the PEM block is password encrypted |
| 99 | // according to RFC 1423. |
| 100 | // |
| 101 | // Deprecated: Legacy PEM encryption as specified in RFC 1423 is insecure by |
| 102 | // design. Since it does not authenticate the ciphertext, it is vulnerable to |
| 103 | // padding oracle attacks that can let an attacker recover the plaintext. |
Brent Austin | ba3052e | 2015-04-21 16:08:23 -0700 | [diff] [blame] | 104 | func IsEncryptedPEMBlock(b *pem.Block) bool { |
| 105 | _, ok := b.Headers["DEK-Info"] |
| 106 | return ok |
| 107 | } |
| 108 | |
| 109 | // IncorrectPasswordError is returned when an incorrect password is detected. |
| 110 | var IncorrectPasswordError = errors.New("x509: decryption password incorrect") |
| 111 | |
Colin Cross | 1f80552 | 2021-05-14 11:10:59 -0700 | [diff] [blame] | 112 | // DecryptPEMBlock takes a PEM block encrypted according to RFC 1423 and the |
| 113 | // password used to encrypt it and returns a slice of decrypted DER encoded |
| 114 | // bytes. It inspects the DEK-Info header to determine the algorithm used for |
| 115 | // decryption. If no DEK-Info header is present, an error is returned. If an |
| 116 | // incorrect password is detected an IncorrectPasswordError is returned. Because |
| 117 | // of deficiencies in the format, it's not always possible to detect an |
| 118 | // incorrect password. In these cases no error will be returned but the |
| 119 | // decrypted DER bytes will be random noise. |
| 120 | // |
| 121 | // Deprecated: Legacy PEM encryption as specified in RFC 1423 is insecure by |
| 122 | // design. Since it does not authenticate the ciphertext, it is vulnerable to |
| 123 | // padding oracle attacks that can let an attacker recover the plaintext. |
Brent Austin | ba3052e | 2015-04-21 16:08:23 -0700 | [diff] [blame] | 124 | func DecryptPEMBlock(b *pem.Block, password []byte) ([]byte, error) { |
| 125 | dek, ok := b.Headers["DEK-Info"] |
| 126 | if !ok { |
| 127 | return nil, errors.New("x509: no DEK-Info header in block") |
| 128 | } |
| 129 | |
Dan Willemsen | bc60c3c | 2021-12-15 01:09:00 -0800 | [diff] [blame] | 130 | mode, hexIV, ok := strings.Cut(dek, ",") |
| 131 | if !ok { |
Brent Austin | ba3052e | 2015-04-21 16:08:23 -0700 | [diff] [blame] | 132 | return nil, errors.New("x509: malformed DEK-Info header") |
| 133 | } |
| 134 | |
Brent Austin | ba3052e | 2015-04-21 16:08:23 -0700 | [diff] [blame] | 135 | ciph := cipherByName(mode) |
| 136 | if ciph == nil { |
| 137 | return nil, errors.New("x509: unknown encryption mode") |
| 138 | } |
| 139 | iv, err := hex.DecodeString(hexIV) |
| 140 | if err != nil { |
| 141 | return nil, err |
| 142 | } |
| 143 | if len(iv) != ciph.blockSize { |
| 144 | return nil, errors.New("x509: incorrect IV size") |
| 145 | } |
| 146 | |
| 147 | // Based on the OpenSSL implementation. The salt is the first 8 bytes |
| 148 | // of the initialization vector. |
| 149 | key := ciph.deriveKey(password, iv[:8]) |
| 150 | block, err := ciph.cipherFunc(key) |
| 151 | if err != nil { |
| 152 | return nil, err |
| 153 | } |
| 154 | |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 155 | if len(b.Bytes)%block.BlockSize() != 0 { |
| 156 | return nil, errors.New("x509: encrypted PEM data is not a multiple of the block size") |
| 157 | } |
| 158 | |
Brent Austin | ba3052e | 2015-04-21 16:08:23 -0700 | [diff] [blame] | 159 | data := make([]byte, len(b.Bytes)) |
| 160 | dec := cipher.NewCBCDecrypter(block, iv) |
| 161 | dec.CryptBlocks(data, b.Bytes) |
| 162 | |
| 163 | // Blocks are padded using a scheme where the last n bytes of padding are all |
| 164 | // equal to n. It can pad from 1 to blocksize bytes inclusive. See RFC 1423. |
| 165 | // For example: |
| 166 | // [x y z 2 2] |
| 167 | // [x y 7 7 7 7 7 7 7] |
| 168 | // If we detect a bad padding, we assume it is an invalid password. |
| 169 | dlen := len(data) |
| 170 | if dlen == 0 || dlen%ciph.blockSize != 0 { |
| 171 | return nil, errors.New("x509: invalid padding") |
| 172 | } |
| 173 | last := int(data[dlen-1]) |
| 174 | if dlen < last { |
| 175 | return nil, IncorrectPasswordError |
| 176 | } |
| 177 | if last == 0 || last > ciph.blockSize { |
| 178 | return nil, IncorrectPasswordError |
| 179 | } |
| 180 | for _, val := range data[dlen-last:] { |
| 181 | if int(val) != last { |
| 182 | return nil, IncorrectPasswordError |
| 183 | } |
| 184 | } |
| 185 | return data[:dlen-last], nil |
| 186 | } |
| 187 | |
| 188 | // EncryptPEMBlock returns a PEM block of the specified type holding the |
Colin Cross | 1f80552 | 2021-05-14 11:10:59 -0700 | [diff] [blame] | 189 | // given DER encoded data encrypted with the specified algorithm and |
| 190 | // password according to RFC 1423. |
| 191 | // |
| 192 | // Deprecated: Legacy PEM encryption as specified in RFC 1423 is insecure by |
| 193 | // design. Since it does not authenticate the ciphertext, it is vulnerable to |
| 194 | // padding oracle attacks that can let an attacker recover the plaintext. |
Brent Austin | ba3052e | 2015-04-21 16:08:23 -0700 | [diff] [blame] | 195 | func EncryptPEMBlock(rand io.Reader, blockType string, data, password []byte, alg PEMCipher) (*pem.Block, error) { |
| 196 | ciph := cipherByKey(alg) |
| 197 | if ciph == nil { |
| 198 | return nil, errors.New("x509: unknown encryption mode") |
| 199 | } |
| 200 | iv := make([]byte, ciph.blockSize) |
| 201 | if _, err := io.ReadFull(rand, iv); err != nil { |
| 202 | return nil, errors.New("x509: cannot generate IV: " + err.Error()) |
| 203 | } |
| 204 | // The salt is the first 8 bytes of the initialization vector, |
| 205 | // matching the key derivation in DecryptPEMBlock. |
| 206 | key := ciph.deriveKey(password, iv[:8]) |
| 207 | block, err := ciph.cipherFunc(key) |
| 208 | if err != nil { |
| 209 | return nil, err |
| 210 | } |
| 211 | enc := cipher.NewCBCEncrypter(block, iv) |
| 212 | pad := ciph.blockSize - len(data)%ciph.blockSize |
| 213 | encrypted := make([]byte, len(data), len(data)+pad) |
| 214 | // We could save this copy by encrypting all the whole blocks in |
| 215 | // the data separately, but it doesn't seem worth the additional |
| 216 | // code. |
| 217 | copy(encrypted, data) |
Colin Cross | d9c6b80 | 2019-03-19 21:10:31 -0700 | [diff] [blame] | 218 | // See RFC 1423, Section 1.1. |
Brent Austin | ba3052e | 2015-04-21 16:08:23 -0700 | [diff] [blame] | 219 | for i := 0; i < pad; i++ { |
| 220 | encrypted = append(encrypted, byte(pad)) |
| 221 | } |
| 222 | enc.CryptBlocks(encrypted, encrypted) |
| 223 | |
| 224 | return &pem.Block{ |
| 225 | Type: blockType, |
| 226 | Headers: map[string]string{ |
| 227 | "Proc-Type": "4,ENCRYPTED", |
| 228 | "DEK-Info": ciph.name + "," + hex.EncodeToString(iv), |
| 229 | }, |
| 230 | Bytes: encrypted, |
| 231 | }, nil |
| 232 | } |
| 233 | |
| 234 | func cipherByName(name string) *rfc1423Algo { |
| 235 | for i := range rfc1423Algos { |
| 236 | alg := &rfc1423Algos[i] |
| 237 | if alg.name == name { |
| 238 | return alg |
| 239 | } |
| 240 | } |
| 241 | return nil |
| 242 | } |
| 243 | |
| 244 | func cipherByKey(key PEMCipher) *rfc1423Algo { |
| 245 | for i := range rfc1423Algos { |
| 246 | alg := &rfc1423Algos[i] |
| 247 | if alg.cipher == key { |
| 248 | return alg |
| 249 | } |
| 250 | } |
| 251 | return nil |
| 252 | } |