Move subtle.go to its own package

subtle/subtle.go

@@ -0,0 +1,33 @@
+package subtle
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+
+	"golang.org/x/crypto/scrypt"
+)
+
+// EncryptWithoutIntegrity encrypts data with AES-CTR. Note: this encryption
+// mode is not secure when stored/sent on an untrusted medium.
+func EncryptWithoutIntegrity(key, input, iv []byte) (output []byte, err error) {
+	var block cipher.Block
+	if block, err = aes.NewCipher(key); err != nil {
+		return
+	}
+	output = make([]byte, len(input))
+	stream := cipher.NewCTR(block, iv)
+	stream.XORKeyStream(output, input)
+	return
+}
+
+// DecryptWithoutIntegrity decrypts data encrypted with AES-CTR.
+func DecryptWithoutIntegrity(key, input, iv []byte) ([]byte, error) {
+	// AES-CTR decryption is identical to encryption.
+	return EncryptWithoutIntegrity(key, input, iv)
+}
+
+// DeriveKey derives a key from a password using scrypt. N should be set to the
+// highest power of 2 you can derive within 100 milliseconds.
+func DeriveKey(password string, salt []byte, N int) ([]byte, error) {
+	return scrypt.Key([]byte(password), salt, N, 8, 1, 32)
+}