Add support for key based encryption and decryption #3
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| Original file line number | Diff line number | Diff line change | ||||
|---|---|---|---|---|---|---|
| @@ -1,139 +1,233 @@ | ||||||
| package rncryptor | ||||||
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| import ( | ||||||
| "bytes" | ||||||
| "crypto/aes" | ||||||
| "crypto/cipher" | ||||||
| "crypto/hmac" | ||||||
| "crypto/rand" | ||||||
| "crypto/sha1" | ||||||
| "crypto/sha256" | ||||||
| "errors" | ||||||
| "fmt" | ||||||
| "golang.org/x/crypto/pbkdf2" | ||||||
| ) | ||||||
|
|
||||||
| const ( | ||||||
| blockSize = 16 | ||||||
| supportedVersion = byte(3) | ||||||
| optionUsesPassword = byte(1) | ||||||
| hmacLength = 32 | ||||||
| saltLength = 8 | ||||||
| pbkdfIterations = 10000 | ||||||
| keyByteLength = 32 | ||||||
| ) | ||||||
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| func Decrypt(password string, data []byte) ([]byte, error) { | ||||||
| version := data[0] | ||||||
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||||||
| if version != supportedVersion { | ||||||
| return nil, errors.New(fmt.Sprintf("unsupported version: %d", version)) | ||||||
| } | ||||||
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| options := data[1] | ||||||
| if options&optionUsesPassword == 0 { | ||||||
| return nil, errors.New("cannot decrypt key-based encryption with password") | ||||||
| } | ||||||
|
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||||||
| encSalt := data[2:10] | ||||||
| hmacSalt := data[10:18] | ||||||
| iv := data[18:34] | ||||||
| cipherText := data[34:(len(data) - hmacLength)] | ||||||
| expectedHmac := data[len(data)-hmacLength:] | ||||||
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| hmacKey := pbkdf2.Key([]byte(password), hmacSalt, pbkdfIterations, keyByteLength, sha1.New) | ||||||
| testHmac := hmac.New(sha256.New, hmacKey) | ||||||
| testHmac.Write(data[:len(data)-hmacLength]) | ||||||
| testHmacVal := testHmac.Sum(nil) | ||||||
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| // its important to use hmac.Equal to not leak time | ||||||
| // information. See https://github.com/RNCryptor/RNCryptor-Spec | ||||||
| verified := hmac.Equal(testHmacVal, expectedHmac) | ||||||
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||||||
| if !verified { | ||||||
| return nil, errors.New("password may be incorrect, or the data has been corrupted: (HMAC could not be verified)") | ||||||
| } | ||||||
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||||||
| cipherKey := pbkdf2.Key([]byte(password), encSalt, pbkdfIterations, keyByteLength, sha1.New) | ||||||
| cipherBlock, err := aes.NewCipher(cipherKey) | ||||||
| if err != nil { | ||||||
| return nil, err | ||||||
| } | ||||||
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||||||
| decrypted := make([]byte, len(cipherText)) | ||||||
| copy(decrypted, cipherText) | ||||||
| decrypter := cipher.NewCBCDecrypter(cipherBlock, iv) | ||||||
| decrypter.CryptBlocks(decrypted, decrypted) | ||||||
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| // un-padd decrypted data | ||||||
| length := len(decrypted) | ||||||
| unpadding := int(decrypted[length-1]) | ||||||
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||||||
| return decrypted[:(length - unpadding)], nil | ||||||
| } | ||||||
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| func DecryptWithKey(decKey, hmacKey, data []byte) ([]byte, error) { | ||||||
| version := data[0] | ||||||
|
There was a problem hiding this comment. same suggestion as above about checking the length before accessing the slice. |
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| if version != supportedVersion { | ||||||
| return nil, errors.New(fmt.Sprintf("unsupported version: %d", version)) | ||||||
|
There was a problem hiding this comment.
Suggested change
|
||||||
| } | ||||||
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| options := data[1] | ||||||
| if options&optionUsesPassword != 0 { | ||||||
| return nil, errors.New("cannot decrypt password-encrypted data with key") | ||||||
| } | ||||||
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| iv := data[2:18] | ||||||
| cipherText := data[18 : len(data)-hmacLength] | ||||||
| expectedHmac := data[len(data)-hmacLength:] | ||||||
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| testHmac := hmac.New(sha256.New, hmacKey) | ||||||
| testHmac.Write(data[:len(data)-32]) | ||||||
| testHmacVal := testHmac.Sum(nil) | ||||||
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| // its important to use hmac.Equal to not leak time | ||||||
| // information. See https://github.com/RNCryptor/RNCryptor-Spec | ||||||
| verified := hmac.Equal(testHmacVal, expectedHmac) | ||||||
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| if !verified { | ||||||
| return nil, errors.New("key may be incorrect, or the data has been corrupted: (HMAC could not be verified)") | ||||||
| } | ||||||
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| cipherBlock, err := aes.NewCipher(decKey) | ||||||
| if err != nil { | ||||||
| return nil, err | ||||||
| } | ||||||
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| decrypted := make([]byte, len(cipherText)) | ||||||
| copy(decrypted, cipherText) | ||||||
| decrypter := cipher.NewCBCDecrypter(cipherBlock, iv) | ||||||
| decrypter.CryptBlocks(decrypted, decrypted) | ||||||
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| // un-padd decrypted data | ||||||
| length := len(decrypted) | ||||||
| unpadding := int(decrypted[length-1]) | ||||||
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| return decrypted[:(length - unpadding)], nil | ||||||
| } | ||||||
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| func Encrypt(password string, data []byte) ([]byte, error) { | ||||||
| encSalt, encSaltErr := RandBytes(saltLength) | ||||||
| if encSaltErr != nil { | ||||||
| return nil, encSaltErr | ||||||
| } | ||||||
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| hmacSalt, hmacSaltErr := RandBytes(saltLength) | ||||||
| if hmacSaltErr != nil { | ||||||
| return nil, hmacSaltErr | ||||||
| } | ||||||
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| iv, ivErr := RandBytes(blockSize) | ||||||
| if ivErr != nil { | ||||||
| return nil, ivErr | ||||||
| } | ||||||
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| encrypted, encErr := EncryptWithOptions(password, data, encSalt, hmacSalt, iv) | ||||||
| if encErr != nil { | ||||||
| return nil, encErr | ||||||
| } | ||||||
| return encrypted, nil | ||||||
| } | ||||||
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| func EncryptWithOptions(password string, data, encSalt, hmacSalt, iv []byte) ([]byte, error) { | ||||||
| if len(password) < 1 { | ||||||
| return nil, errors.New("password cannot be empty") | ||||||
| } | ||||||
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| encKey := pbkdf2.Key([]byte(password), encSalt, pbkdfIterations, keyByteLength, sha1.New) | ||||||
| hmacKey := pbkdf2.Key([]byte(password), hmacSalt, pbkdfIterations, keyByteLength, sha1.New) | ||||||
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| version := supportedVersion | ||||||
| options := optionUsesPassword | ||||||
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| msg := make([]byte, 0) | ||||||
| msg = append(msg, version) | ||||||
| msg = append(msg, options) | ||||||
| msg = append(msg, encSalt...) | ||||||
| msg = append(msg, hmacSalt...) | ||||||
| msg = append(msg, iv...) | ||||||
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| ciphertext, hmacValue, err := encryptAndHmac(msg, data, iv, encKey, hmacKey) | ||||||
| if err != nil { | ||||||
| return nil, err | ||||||
| } | ||||||
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| msg = append(msg, ciphertext...) | ||||||
| msg = append(msg, hmacValue...) | ||||||
| return msg, nil | ||||||
| } | ||||||
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| func EncryptWithKey(encKey, hmacKey, data []byte) ([]byte, error) { | ||||||
| iv, err := RandBytes(blockSize) | ||||||
| if err != nil { | ||||||
| return nil, err | ||||||
| } | ||||||
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| return EncryptWithKeyAndIv(encKey, hmacKey, iv, data) | ||||||
| } | ||||||
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| func EncryptWithKeyAndIv(encKey, hmacKey, iv, data []byte) ([]byte, error) { | ||||||
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| version := supportedVersion | ||||||
| options := byte(0) | ||||||
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| msg := make([]byte, 0) | ||||||
| msg = append(msg, version) | ||||||
| msg = append(msg, options) | ||||||
| msg = append(msg, iv...) | ||||||
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| ciphertext, hmacValue, err := encryptAndHmac(msg, data, iv, encKey, hmacKey) | ||||||
| if err != nil { | ||||||
| return nil, err | ||||||
| } | ||||||
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| msg = append(msg, ciphertext...) | ||||||
| msg = append(msg, hmacValue...) | ||||||
| return msg, nil | ||||||
| } | ||||||
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| func encryptAndHmac(header, data, iv, encKey, hmacKey []byte) ([]byte, []byte, error) { | ||||||
| cipherBlock, err := aes.NewCipher(encKey) | ||||||
| if err != nil { | ||||||
| return nil, nil, err | ||||||
| } | ||||||
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| // pad text for encryption | ||||||
| cipherText := make([]byte, len(data)) | ||||||
| copy(cipherText, data) | ||||||
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| padding := blockSize - (len(cipherText) % blockSize) | ||||||
| padText := bytes.Repeat([]byte{byte(padding)}, padding) | ||||||
| cipherText = append(cipherText, padText...) | ||||||
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| encrypter := cipher.NewCBCEncrypter(cipherBlock, iv) | ||||||
| encrypter.CryptBlocks(cipherText, cipherText) | ||||||
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| msg := append(header, cipherText...) | ||||||
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| hmacSrc := hmac.New(sha256.New, hmacKey) | ||||||
| hmacSrc.Write(msg) | ||||||
| hmacVal := hmacSrc.Sum(nil) | ||||||
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| return cipherText, hmacVal, nil | ||||||
| } | ||||||
|
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| func RandBytes(num int64) ([]byte, error) { | ||||||
| bits := make([]byte, num) | ||||||
| _, err := rand.Read(bits) | ||||||
| if err != nil { | ||||||
| return nil, err | ||||||
| } | ||||||
| return bits, nil | ||||||
| } | ||||||
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This is one of the causes of #1 I think, but it might be nice to check the length up front and return an error if the length is shorter than the expected header instead of causing a panic.
Possibly something like: