internal/subtle: rename to internal/alias

This avoids an import conflict in code that needs to import
crypto/subtle as well.

CL 424194 does the same for the main repo.

Change-Id: Ic54cb62bbfdcf5c2cb6f15ac47075ee1c41981ad
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/424175
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Russ Cox <rsc@golang.org>

xts/xts.go

@@ -29,7 +29,7 @@ import (
 	"errors"
 	"sync"
 
-	"golang.org/x/crypto/internal/subtle"
+	"golang.org/x/crypto/internal/alias"
 )
 
 // Cipher contains an expanded key structure. It is safe for concurrent use if
@@ -75,7 +75,7 @@ func (c *Cipher) Encrypt(ciphertext, plaintext []byte, sectorNum uint64) {
 	if len(plaintext)%blockSize != 0 {
 		panic("xts: plaintext is not a multiple of the block size")
 	}
-	if subtle.InexactOverlap(ciphertext[:len(plaintext)], plaintext) {
+	if alias.InexactOverlap(ciphertext[:len(plaintext)], plaintext) {
 		panic("xts: invalid buffer overlap")
 	}
 
@@ -114,7 +114,7 @@ func (c *Cipher) Decrypt(plaintext, ciphertext []byte, sectorNum uint64) {
 	if len(ciphertext)%blockSize != 0 {
 		panic("xts: ciphertext is not a multiple of the block size")
 	}
-	if subtle.InexactOverlap(plaintext[:len(ciphertext)], ciphertext) {
+	if alias.InexactOverlap(plaintext[:len(ciphertext)], ciphertext) {
 		panic("xts: invalid buffer overlap")
 	}