Switch to keybase go-crypto (for some elliptic curve key) + test (#1925)

* Switch to keybase go-crypto (for some elliptic curve key) + test

* Use assert.NoError 

and add a little more context to failing test description

* Use assert.(No)Error everywhere 🌈

and assert.Error in place of .Nil/.NotNil

vendor/github.com/keybase/go-crypto/openpgp/packet/ocfb.go

@@ -0,0 +1,143 @@
+// Copyright 2010 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.
+
+// OpenPGP CFB Mode. http://tools.ietf.org/html/rfc4880#section-13.9
+
+package packet
+
+import (
+	"crypto/cipher"
+)
+
+type ocfbEncrypter struct {
+	b       cipher.Block
+	fre     []byte
+	outUsed int
+}
+
+// An OCFBResyncOption determines if the "resynchronization step" of OCFB is
+// performed.
+type OCFBResyncOption bool
+
+const (
+	OCFBResync   OCFBResyncOption = true
+	OCFBNoResync OCFBResyncOption = false
+)
+
+// NewOCFBEncrypter returns a cipher.Stream which encrypts data with OpenPGP's
+// cipher feedback mode using the given cipher.Block, and an initial amount of
+// ciphertext.  randData must be random bytes and be the same length as the
+// cipher.Block's block size. Resync determines if the "resynchronization step"
+// from RFC 4880, 13.9 step 7 is performed. Different parts of OpenPGP vary on
+// this point.
+func NewOCFBEncrypter(block cipher.Block, randData []byte, resync OCFBResyncOption) (cipher.Stream, []byte) {
+	blockSize := block.BlockSize()
+	if len(randData) != blockSize {
+		return nil, nil
+	}
+
+	x := &ocfbEncrypter{
+		b:       block,
+		fre:     make([]byte, blockSize),
+		outUsed: 0,
+	}
+	prefix := make([]byte, blockSize+2)
+
+	block.Encrypt(x.fre, x.fre)
+	for i := 0; i < blockSize; i++ {
+		prefix[i] = randData[i] ^ x.fre[i]
+	}
+
+	block.Encrypt(x.fre, prefix[:blockSize])
+	prefix[blockSize] = x.fre[0] ^ randData[blockSize-2]
+	prefix[blockSize+1] = x.fre[1] ^ randData[blockSize-1]
+
+	if resync {
+		block.Encrypt(x.fre, prefix[2:])
+	} else {
+		x.fre[0] = prefix[blockSize]
+		x.fre[1] = prefix[blockSize+1]
+		x.outUsed = 2
+	}
+	return x, prefix
+}
+
+func (x *ocfbEncrypter) XORKeyStream(dst, src []byte) {
+	for i := 0; i < len(src); i++ {
+		if x.outUsed == len(x.fre) {
+			x.b.Encrypt(x.fre, x.fre)
+			x.outUsed = 0
+		}
+
+		x.fre[x.outUsed] ^= src[i]
+		dst[i] = x.fre[x.outUsed]
+		x.outUsed++
+	}
+}
+
+type ocfbDecrypter struct {
+	b       cipher.Block
+	fre     []byte
+	outUsed int
+}
+
+// NewOCFBDecrypter returns a cipher.Stream which decrypts data with OpenPGP's
+// cipher feedback mode using the given cipher.Block. Prefix must be the first
+// blockSize + 2 bytes of the ciphertext, where blockSize is the cipher.Block's
+// block size. If an incorrect key is detected then nil is returned. On
+// successful exit, blockSize+2 bytes of decrypted data are written into
+// prefix. Resync determines if the "resynchronization step" from RFC 4880,
+// 13.9 step 7 is performed. Different parts of OpenPGP vary on this point.
+func NewOCFBDecrypter(block cipher.Block, prefix []byte, resync OCFBResyncOption) cipher.Stream {
+	blockSize := block.BlockSize()
+	if len(prefix) != blockSize+2 {
+		return nil
+	}
+
+	x := &ocfbDecrypter{
+		b:       block,
+		fre:     make([]byte, blockSize),
+		outUsed: 0,
+	}
+	prefixCopy := make([]byte, len(prefix))
+	copy(prefixCopy, prefix)
+
+	block.Encrypt(x.fre, x.fre)
+	for i := 0; i < blockSize; i++ {
+		prefixCopy[i] ^= x.fre[i]
+	}
+
+	block.Encrypt(x.fre, prefix[:blockSize])
+	prefixCopy[blockSize] ^= x.fre[0]
+	prefixCopy[blockSize+1] ^= x.fre[1]
+
+	if prefixCopy[blockSize-2] != prefixCopy[blockSize] ||
+		prefixCopy[blockSize-1] != prefixCopy[blockSize+1] {
+		return nil
+	}
+
+	if resync {
+		block.Encrypt(x.fre, prefix[2:])
+	} else {
+		x.fre[0] = prefix[blockSize]
+		x.fre[1] = prefix[blockSize+1]
+		x.outUsed = 2
+	}
+	copy(prefix, prefixCopy)
+	return x
+}
+
+func (x *ocfbDecrypter) XORKeyStream(dst, src []byte) {
+	for i := 0; i < len(src); i++ {
+		if x.outUsed == len(x.fre) {
+			x.b.Encrypt(x.fre, x.fre)
+			x.outUsed = 0
+		}
+
+		c := src[i]
+		dst[i] = x.fre[x.outUsed] ^ src[i]
+		x.fre[x.outUsed] = c
+		x.outUsed++
+	}
+}