Add babyjub from go-iden3/crypto/babyjub

babyjub/helpers.go

@@ -0,0 +1,39 @@
+package babyjub
+
+import (
+	"github.com/dchest/blake512" // I have personally reviewed that this module doesn't do anything suspicious
+	"math/big"
+)
+
+// SwapEndianness swaps the endianness of the value encoded in xs.  If xs is
+// Big-Endian, the result will be Little-Endian and viceversa.
+func SwapEndianness(xs []byte) []byte {
+	ys := make([]byte, len(xs))
+	for i, b := range xs {
+		ys[len(xs)-1-i] = b
+	}
+	return ys
+}
+
+// BigIntLEBytes encodes a big.Int into an array in Little-Endian.
+func BigIntLEBytes(v *big.Int) [32]byte {
+	le := SwapEndianness(v.Bytes())
+	res := [32]byte{}
+	copy(res[:], le)
+	return res
+}
+
+// SetBigIntFromLEBytes sets the value of a big.Int from a Little-Endian
+// encoded value.
+func SetBigIntFromLEBytes(v *big.Int, leBuf []byte) *big.Int {
+	beBuf := SwapEndianness(leBuf)
+	return v.SetBytes(beBuf)
+}
+
+// Blake512 performs the blake-512 hash over the buffer m.  Note that this is
+// the original blake from the SHA3 competition and not the new blake2 version.
+func Blake512(m []byte) []byte {
+	h := blake512.New()
+	h.Write(m[:])
+	return h.Sum(nil)
+}