aes: encrypt and decrypt one block at a time

cng/aes.go

@@ -41,15 +41,20 @@ func (c *aesCipher) finalize() {
 func (c *aesCipher) BlockSize() int { return aesBlockSize }
 
 func (c *aesCipher) Encrypt(dst, src []byte) {
-	if subtle.InexactOverlap(dst, src) {
-		panic("crypto/cipher: invalid buffer overlap")
-	}
 	if len(src) < aesBlockSize {
 		panic("crypto/aes: input not full block")
 	}
 	if len(dst) < aesBlockSize {
 		panic("crypto/aes: output not full block")
 	}
+
+	// cypher.Block.Encrypt() is documented to encrypt one full block
+	// at a time, so we truncate the input and output to the block size.
+	dst, src = dst[:aesBlockSize], src[:aesBlockSize]
+	if subtle.InexactOverlap(dst, src) {
+		panic("crypto/cipher: invalid buffer overlap")
+	}
+
 	var ret uint32
 	err := bcrypt.Encrypt(c.kh, src, nil, nil, dst, &ret, 0)
 	if err != nil {
@@ -62,16 +67,20 @@ func (c *aesCipher) Encrypt(dst, src []byte) {
 }
 
 func (c *aesCipher) Decrypt(dst, src []byte) {
-	if subtle.InexactOverlap(dst, src) {
-		panic("crypto/cipher: invalid buffer overlap")
-	}
 	if len(src) < aesBlockSize {
 		panic("crypto/aes: input not full block")
 	}
 	if len(dst) < aesBlockSize {
 		panic("crypto/aes: output not full block")
 	}
 
+	// cypher.Block.Decrypt() is documented to decrypt one full block
+	// at a time, so we truncate the input and output to the block size.
+	dst, src = dst[:aesBlockSize], src[:aesBlockSize]
+	if subtle.InexactOverlap(dst, src) {
+		panic("crypto/cipher: invalid buffer overlap")
+	}
+
 	var ret uint32
 	err := bcrypt.Decrypt(c.kh, src, nil, nil, dst, &ret, 0)
 	if err != nil {

cng/aes_test.go

@@ -9,7 +9,10 @@ package cng
 import (
 	"bytes"
 	"crypto/cipher"
+	"fmt"
 	"testing"
+
+	"github.com/microsoft/go-crypto-winnative/internal/cryptotest"
 )
 
 var key = []byte("D249BF6DEC97B1EBD69BC4D6B3A3C49D")
@@ -375,3 +378,12 @@ func TestCBCDecryptSimple(t *testing.T) {
 		t.Errorf("decryption incorrect\nexp %v, got %v\n", plainText, decrypted)
 	}
 }
+
+// Test AES against the general cipher.Block interface tester.
+func TestAESBlock(t *testing.T) {
+	for _, keylen := range []int{128, 192, 256} {
+		t.Run(fmt.Sprintf("AES-%d", keylen), func(t *testing.T) {
+			cryptotest.TestBlock(t, keylen/8, NewAESCipher)
+		})
+	}
+}