all: make overlap rules wording consistent

Updates golang/go#21279

Change-Id: I686835c644f52e3d5ea2b7e6431ef096d188c19d
Reviewed-on: https://go-review.googlesource.com/61133
Reviewed-by: Ian Lance Taylor <iant@golang.org>

chacha20poly1305/internal/chacha20/chacha_generic.go

@@ -167,9 +167,8 @@ func core(out *[64]byte, in *[16]byte, k *[32]byte) {
 }
 
 // XORKeyStream crypts bytes from in to out using the given key and counters.
-// In and out may be the same slice but otherwise should not overlap. Counter
-// contains the raw ChaCha20 counter bytes (i.e. block counter followed by
-// nonce).
+// In and out must overlap entirely or not at all. Counter contains the raw
+// ChaCha20 counter bytes (i.e. block counter followed by nonce).
 func XORKeyStream(out, in []byte, counter *[16]byte, key *[32]byte) {
 	var block [64]byte
 	var counterCopy [16]byte

nacl/box/box.go

@@ -73,7 +73,7 @@ func Precompute(sharedKey, peersPublicKey, privateKey *[32]byte) {
 }
 
 // Seal appends an encrypted and authenticated copy of message to out, which
-// will be Overhead bytes longer than the original and must not overlap. The
+// will be Overhead bytes longer than the original and must not overlap it. The
 // nonce must be unique for each distinct message for a given pair of keys.
 func Seal(out, message []byte, nonce *[24]byte, peersPublicKey, privateKey *[32]byte) []byte {
 	var sharedKey [32]byte

salsa20/salsa/salsa20_amd64.go

@@ -13,7 +13,7 @@ package salsa
 func salsa2020XORKeyStream(out, in *byte, n uint64, nonce, key *byte)
 
 // XORKeyStream crypts bytes from in to out using the given key and counters.
-// In and out may be the same slice but otherwise should not overlap. Counter
+// In and out must overlap entirely or not at all. Counter
 // contains the raw salsa20 counter bytes (both nonce and block counter).
 func XORKeyStream(out, in []byte, counter *[16]byte, key *[32]byte) {
 	if len(in) == 0 {

salsa20/salsa/salsa20_ref.go

@@ -203,7 +203,7 @@ func core(out *[64]byte, in *[16]byte, k *[32]byte, c *[16]byte) {
 }
 
 // XORKeyStream crypts bytes from in to out using the given key and counters.
-// In and out may be the same slice but otherwise should not overlap. Counter
+// In and out must overlap entirely or not at all. Counter
 // contains the raw salsa20 counter bytes (both nonce and block counter).
 func XORKeyStream(out, in []byte, counter *[16]byte, key *[32]byte) {
 	var block [64]byte

salsa20/salsa20.go

@@ -27,8 +27,8 @@ import (
 	"golang.org/x/crypto/salsa20/salsa"
 )
 
-// XORKeyStream crypts bytes from in to out using the given key and nonce. In
-// and out may be the same slice but otherwise should not overlap. Nonce must
+// XORKeyStream crypts bytes from in to out using the given key and nonce.
+// In and out must overlap entirely or not at all. Nonce must
 // be either 8 or 24 bytes long.
 func XORKeyStream(out, in []byte, nonce []byte, key *[32]byte) {
 	if len(out) < len(in) {

xts/xts.go

@@ -55,7 +55,7 @@ func NewCipher(cipherFunc func([]byte) (cipher.Block, error), key []byte) (c *Ci
 }
 
 // Encrypt encrypts a sector of plaintext and puts the result into ciphertext.
-// Plaintext and ciphertext may be the same slice but should not overlap.
+// Plaintext and ciphertext must overlap entirely or not at all.
 // Sectors must be a multiple of 16 bytes and less than 2²⁴ bytes.
 func (c *Cipher) Encrypt(ciphertext, plaintext []byte, sectorNum uint64) {
 	if len(ciphertext) < len(plaintext) {
@@ -86,7 +86,7 @@ func (c *Cipher) Encrypt(ciphertext, plaintext []byte, sectorNum uint64) {
 }
 
 // Decrypt decrypts a sector of ciphertext and puts the result into plaintext.
-// Plaintext and ciphertext may be the same slice but should not overlap.
+// Plaintext and ciphertext must overlap entirely or not at all.
 // Sectors must be a multiple of 16 bytes and less than 2²⁴ bytes.
 func (c *Cipher) Decrypt(plaintext, ciphertext []byte, sectorNum uint64) {
 	if len(plaintext) < len(ciphertext) {