vendor golang.org/x/crypto using glide

This would help us build go-mtree on RHEL/CentOS and
distros where golang.org/x/crypto isn't provided or supported.

Signed-off-by: Lokesh Mandvekar <lsm5@fedoraproject.org>

vendor/golang.org/x/crypto/salsa20/salsa20.go

@@ -0,0 +1,54 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+/*
+Package salsa20 implements the Salsa20 stream cipher as specified in http://cr.yp.to/snuffle/spec.pdf.
+
+Salsa20 differs from many other stream ciphers in that it is message orientated
+rather than byte orientated. Keystream blocks are not preserved between calls,
+therefore each side must encrypt/decrypt data with the same segmentation.
+
+Another aspect of this difference is that part of the counter is exposed as
+an nonce in each call. Encrypting two different messages with the same (key,
+nonce) pair leads to trivial plaintext recovery. This is analogous to
+encrypting two different messages with the same key with a traditional stream
+cipher.
+
+This package also implements XSalsa20: a version of Salsa20 with a 24-byte
+nonce as specified in http://cr.yp.to/snuffle/xsalsa-20081128.pdf. Simply
+passing a 24-byte slice as the nonce triggers XSalsa20.
+*/
+package salsa20 // import "golang.org/x/crypto/salsa20"
+
+// TODO(agl): implement XORKeyStream12 and XORKeyStream8 - the reduced round variants of Salsa20.
+
+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
+// be either 8 or 24 bytes long.
+func XORKeyStream(out, in []byte, nonce []byte, key *[32]byte) {
+	if len(out) < len(in) {
+		in = in[:len(out)]
+	}
+
+	var subNonce [16]byte
+
+	if len(nonce) == 24 {
+		var subKey [32]byte
+		var hNonce [16]byte
+		copy(hNonce[:], nonce[:16])
+		salsa.HSalsa20(&subKey, &hNonce, key, &salsa.Sigma)
+		copy(subNonce[:], nonce[16:])
+		key = &subKey
+	} else if len(nonce) == 8 {
+		copy(subNonce[:], nonce[:])
+	} else {
+		panic("salsa20: nonce must be 8 or 24 bytes")
+	}
+
+	salsa.XORKeyStream(out, in, &subNonce, key)
+}