122 lines
3 KiB
Go
122 lines
3 KiB
Go
package dhutil
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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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"errors"
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"fmt"
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"io"
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"golang.org/x/crypto/curve25519"
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)
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type PublicKeyInfo struct {
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Curve25519PublicKey []byte `json:"curve25519_public_key"`
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}
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type Envelope struct {
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Curve25519PublicKey []byte `json:"curve25519_public_key"`
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Nonce []byte `json:"nonce"`
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EncryptedPayload []byte `json:"encrypted_payload"`
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}
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// generatePublicPrivateKey uses curve25519 to generate a public and private key
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// pair.
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func GeneratePublicPrivateKey() ([]byte, []byte, error) {
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var scalar, public [32]byte
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if _, err := io.ReadFull(rand.Reader, scalar[:]); err != nil {
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return nil, nil, err
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}
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curve25519.ScalarBaseMult(&public, &scalar)
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return public[:], scalar[:], nil
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}
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// generateSharedKey uses the private key and the other party's public key to
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// generate the shared secret.
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func GenerateSharedKey(ourPrivate, theirPublic []byte) ([]byte, error) {
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if len(ourPrivate) != 32 {
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return nil, fmt.Errorf("invalid private key length: %d", len(ourPrivate))
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}
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if len(theirPublic) != 32 {
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return nil, fmt.Errorf("invalid public key length: %d", len(theirPublic))
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}
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var scalar, pub, secret [32]byte
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copy(scalar[:], ourPrivate)
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copy(pub[:], theirPublic)
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curve25519.ScalarMult(&secret, &scalar, &pub)
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return secret[:], nil
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}
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// Use AES256-GCM to encrypt some plaintext with a provided key. The returned values are
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// the ciphertext, the nonce, and error respectively.
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func EncryptAES(key, plaintext, aad []byte) ([]byte, []byte, error) {
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// We enforce AES-256, so check explicitly for 32 bytes on the key
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if len(key) != 32 {
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return nil, nil, fmt.Errorf("invalid key length: %d", len(key))
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}
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if len(plaintext) == 0 {
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return nil, nil, errors.New("empty plaintext provided")
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}
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block, err := aes.NewCipher(key)
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if err != nil {
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return nil, nil, err
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}
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// Never use more than 2^32 random nonces with a given key because of the risk of a repeat.
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nonce := make([]byte, 12)
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if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
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return nil, nil, 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 nil, nil, err
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}
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ciphertext := aesgcm.Seal(nil, nonce, plaintext, aad)
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return ciphertext, nonce, nil
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}
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// Use AES256-GCM to decrypt some ciphertext with a provided key and nonce. The
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// returned values are the plaintext and error respectively.
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func DecryptAES(key, ciphertext, nonce, aad []byte) ([]byte, error) {
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// We enforce AES-256, so check explicitly for 32 bytes on the key
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if len(key) != 32 {
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return nil, fmt.Errorf("invalid key length: %d", len(key))
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}
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if len(ciphertext) == 0 {
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return nil, errors.New("empty ciphertext provided")
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}
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if len(nonce) == 0 {
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return nil, errors.New("empty nonce provided")
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}
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block, err := aes.NewCipher(key)
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if err != nil {
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return nil, 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 nil, err
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}
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plaintext, err := aesgcm.Open(nil, nonce, ciphertext, aad)
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if err != nil {
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return nil, err
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}
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return plaintext, nil
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}
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