mirror of
https://github.com/binwiederhier/ntfy.git
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90 lines
2.5 KiB
Go
90 lines
2.5 KiB
Go
package crypto
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import (
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"crypto/aes"
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"crypto/cipher"
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"crypto/rand"
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"encoding/base64"
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"errors"
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"io"
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)
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const (
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versionByte = 0x31 // "1"
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gcmTagSize = 16
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gcmNonceSize = 12
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)
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var (
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errCiphertextTooShort = errors.New("ciphertext too short")
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errCiphertextUnexpectedVersion = errors.New("unsupported ciphertext version")
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)
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// Encrypt encrypts the given plaintext with the given key using AES-GCM,
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// and encodes the (version, tag, nonce, ciphertext) set as base64.
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//
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// The output format is (|| means concatenate):
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// "1" || tag (128 bits) || IV/nonce (96 bits) || ciphertext (remaining)
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//
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// This format is compatible with Pushbullet's encryption format.
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// See https://docs.pushbullet.com/#encryption for details.
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func Encrypt(plaintext string, key []byte) (string, error) {
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nonce := make([]byte, gcmNonceSize) // Never use more than 2^32 random nonces
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if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
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return "", err
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}
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return encryptWithNonce(plaintext, nonce, key)
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}
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func encryptWithNonce(plaintext string, nonce, key []byte) (string, error) {
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block, err := aes.NewCipher(key)
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if err != nil {
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return "", err
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}
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aesgcm, err := cipher.NewGCM(block)
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if err != nil {
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return "", err
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}
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ciphertextWithTag := aesgcm.Seal(nil, nonce, []byte(plaintext), nil)
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tagIndex := len(ciphertextWithTag) - gcmTagSize
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ciphertext, tag := ciphertextWithTag[:tagIndex], ciphertextWithTag[tagIndex:]
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output := appendSlices([]byte{versionByte}, tag, nonce, ciphertext)
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return base64.StdEncoding.EncodeToString(output), nil
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}
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// Decrypt decodes and decrypts a message that was encrypted with the Encrypt function.
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func Decrypt(input string, key []byte) (string, error) {
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inputBytes, err := base64.StdEncoding.DecodeString(input)
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if err != nil {
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return "", err
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}
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if len(inputBytes) < 1+gcmTagSize+gcmNonceSize {
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return "", errCiphertextTooShort
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}
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version, tag, nonce, ciphertext := inputBytes[0], inputBytes[1:gcmTagSize+1], inputBytes[1+gcmTagSize:1+gcmTagSize+gcmNonceSize], inputBytes[1+gcmTagSize+gcmNonceSize:]
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if version != versionByte {
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return "", errCiphertextUnexpectedVersion
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}
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cipherTextWithTag := append(ciphertext, tag...)
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block, err := aes.NewCipher(key)
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if err != nil {
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return "", err
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}
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aesgcm, err := cipher.NewGCM(block)
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if err != nil {
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return "", err
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}
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plaintext, err := aesgcm.Open(nil, nonce, cipherTextWithTag, nil)
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if err != nil {
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return "", err
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}
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return string(plaintext), nil
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}
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func appendSlices(s ...[]byte) []byte {
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var output []byte
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for _, r := range s {
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output = append(output, r...)
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}
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return output
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}
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