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diff --git a/vendor/golang.org/x/crypto/nacl/secretbox/secretbox.go b/vendor/golang.org/x/crypto/nacl/secretbox/secretbox.go
new file mode 100644
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+++ b/vendor/golang.org/x/crypto/nacl/secretbox/secretbox.go
@@ -0,0 +1,173 @@
+// 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 secretbox encrypts and authenticates small messages.
+
+Secretbox uses XSalsa20 and Poly1305 to encrypt and authenticate messages with
+secret-key cryptography. The length of messages is not hidden.
+
+It is the caller's responsibility to ensure the uniqueness of nonces—for
+example, by using nonce 1 for the first message, nonce 2 for the second
+message, etc. Nonces are long enough that randomly generated nonces have
+negligible risk of collision.
+
+Messages should be small because:
+
+1. The whole message needs to be held in memory to be processed.
+
+2. Using large messages pressures implementations on small machines to decrypt
+and process plaintext before authenticating it. This is very dangerous, and
+this API does not allow it, but a protocol that uses excessive message sizes
+might present some implementations with no other choice.
+
+3. Fixed overheads will be sufficiently amortised by messages as small as 8KB.
+
+4. Performance may be improved by working with messages that fit into data caches.
+
+Thus large amounts of data should be chunked so that each message is small.
+(Each message still needs a unique nonce.) If in doubt, 16KB is a reasonable
+chunk size.
+
+This package is interoperable with NaCl: https://nacl.cr.yp.to/secretbox.html.
+*/
+package secretbox // import "golang.org/x/crypto/nacl/secretbox"
+
+import (
+	"golang.org/x/crypto/internal/subtle"
+	"golang.org/x/crypto/poly1305"
+	"golang.org/x/crypto/salsa20/salsa"
+)
+
+// Overhead is the number of bytes of overhead when boxing a message.
+const Overhead = poly1305.TagSize
+
+// setup produces a sub-key and Salsa20 counter given a nonce and key.
+func setup(subKey *[32]byte, counter *[16]byte, nonce *[24]byte, key *[32]byte) {
+	// We use XSalsa20 for encryption so first we need to generate a
+	// key and nonce with HSalsa20.
+	var hNonce [16]byte
+	copy(hNonce[:], nonce[:])
+	salsa.HSalsa20(subKey, &hNonce, key, &salsa.Sigma)
+
+	// The final 8 bytes of the original nonce form the new nonce.
+	copy(counter[:], nonce[16:])
+}
+
+// sliceForAppend takes a slice and a requested number of bytes. It returns a
+// slice with the contents of the given slice followed by that many bytes and a
+// second slice that aliases into it and contains only the extra bytes. If the
+// original slice has sufficient capacity then no allocation is performed.
+func sliceForAppend(in []byte, n int) (head, tail []byte) {
+	if total := len(in) + n; cap(in) >= total {
+		head = in[:total]
+	} else {
+		head = make([]byte, total)
+		copy(head, in)
+	}
+	tail = head[len(in):]
+	return
+}
+
+// Seal appends an encrypted and authenticated copy of message to out, which
+// must not overlap message. The key and nonce pair must be unique for each
+// distinct message and the output will be Overhead bytes longer than message.
+func Seal(out, message []byte, nonce *[24]byte, key *[32]byte) []byte {
+	var subKey [32]byte
+	var counter [16]byte
+	setup(&subKey, &counter, nonce, key)
+
+	// The Poly1305 key is generated by encrypting 32 bytes of zeros. Since
+	// Salsa20 works with 64-byte blocks, we also generate 32 bytes of
+	// keystream as a side effect.
+	var firstBlock [64]byte
+	salsa.XORKeyStream(firstBlock[:], firstBlock[:], &counter, &subKey)
+
+	var poly1305Key [32]byte
+	copy(poly1305Key[:], firstBlock[:])
+
+	ret, out := sliceForAppend(out, len(message)+poly1305.TagSize)
+	if subtle.AnyOverlap(out, message) {
+		panic("nacl: invalid buffer overlap")
+	}
+
+	// We XOR up to 32 bytes of message with the keystream generated from
+	// the first block.
+	firstMessageBlock := message
+	if len(firstMessageBlock) > 32 {
+		firstMessageBlock = firstMessageBlock[:32]
+	}
+
+	tagOut := out
+	out = out[poly1305.TagSize:]
+	for i, x := range firstMessageBlock {
+		out[i] = firstBlock[32+i] ^ x
+	}
+	message = message[len(firstMessageBlock):]
+	ciphertext := out
+	out = out[len(firstMessageBlock):]
+
+	// Now encrypt the rest.
+	counter[8] = 1
+	salsa.XORKeyStream(out, message, &counter, &subKey)
+
+	var tag [poly1305.TagSize]byte
+	poly1305.Sum(&tag, ciphertext, &poly1305Key)
+	copy(tagOut, tag[:])
+
+	return ret
+}
+
+// Open authenticates and decrypts a box produced by Seal and appends the
+// message to out, which must not overlap box. The output will be Overhead
+// bytes smaller than box.
+func Open(out, box []byte, nonce *[24]byte, key *[32]byte) ([]byte, bool) {
+	if len(box) < Overhead {
+		return nil, false
+	}
+
+	var subKey [32]byte
+	var counter [16]byte
+	setup(&subKey, &counter, nonce, key)
+
+	// The Poly1305 key is generated by encrypting 32 bytes of zeros. Since
+	// Salsa20 works with 64-byte blocks, we also generate 32 bytes of
+	// keystream as a side effect.
+	var firstBlock [64]byte
+	salsa.XORKeyStream(firstBlock[:], firstBlock[:], &counter, &subKey)
+
+	var poly1305Key [32]byte
+	copy(poly1305Key[:], firstBlock[:])
+	var tag [poly1305.TagSize]byte
+	copy(tag[:], box)
+
+	if !poly1305.Verify(&tag, box[poly1305.TagSize:], &poly1305Key) {
+		return nil, false
+	}
+
+	ret, out := sliceForAppend(out, len(box)-Overhead)
+	if subtle.AnyOverlap(out, box) {
+		panic("nacl: invalid buffer overlap")
+	}
+
+	// We XOR up to 32 bytes of box with the keystream generated from
+	// the first block.
+	box = box[Overhead:]
+	firstMessageBlock := box
+	if len(firstMessageBlock) > 32 {
+		firstMessageBlock = firstMessageBlock[:32]
+	}
+	for i, x := range firstMessageBlock {
+		out[i] = firstBlock[32+i] ^ x
+	}
+
+	box = box[len(firstMessageBlock):]
+	out = out[len(firstMessageBlock):]
+
+	// Now decrypt the rest.
+	counter[8] = 1
+	salsa.XORKeyStream(out, box, &counter, &subKey)
+
+	return ret, true
+}