Add crypto dependencies/vendoring

Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>

vendor/github.com/miscreant/miscreant-go/block/block.go

@@ -0,0 +1,49 @@
+// Common block cipher functionality shared across this library
+
+package block
+
+import (
+	"crypto/cipher"
+	"crypto/subtle"
+)
+
+const (
+	// Size of an AES block in bytes
+	Size = 16
+
+	// R is the minimal irreducible polynomial for a 128-bit block size
+	R = 0x87
+)
+
+// Block is a 128-bit array used by certain block ciphers (i.e. AES)
+type Block [Size]byte
+
+// Clear zeroes out the contents of the block
+func (b *Block) Clear() {
+	// TODO: use a more secure zeroing method that won't be optimized away
+	for i := range b {
+		b[i] = 0
+	}
+}
+
+// Dbl performs a doubling of a block over GF(2^128):
+//
+//     a<<1 if firstbit(a)=0
+//     (a<<1) ⊕ 0¹²⁰10000111 if firstbit(a)=1
+//
+func (b *Block) Dbl() {
+	var z byte
+
+	for i := Size - 1; i >= 0; i-- {
+		zz := b[i] >> 7
+		b[i] = b[i]<<1 | z
+		z = zz
+	}
+
+	b[Size-1] ^= byte(subtle.ConstantTimeSelect(int(z), R, 0))
+}
+
+// Encrypt a block with the given block cipher
+func (b *Block) Encrypt(c cipher.Block) {
+	c.Encrypt(b[:], b[:])
+}