#205: Work on supporting OpenID Connect for auth

vendor/gopkg.in/square/go-jose.v2/cipher/ecdh_es.go

@@ -0,0 +1,86 @@
+/*-
+ * Copyright 2014 Square Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package josecipher
+
+import (
+	"bytes"
+	"crypto"
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"encoding/binary"
+)
+
+// DeriveECDHES derives a shared encryption key using ECDH/ConcatKDF as described in JWE/JWA.
+// It is an error to call this function with a private/public key that are not on the same
+// curve. Callers must ensure that the keys are valid before calling this function. Output
+// size may be at most 1<<16 bytes (64 KiB).
+func DeriveECDHES(alg string, apuData, apvData []byte, priv *ecdsa.PrivateKey, pub *ecdsa.PublicKey, size int) []byte {
+	if size > 1<<16 {
+		panic("ECDH-ES output size too large, must be less than or equal to 1<<16")
+	}
+
+	// algId, partyUInfo, partyVInfo inputs must be prefixed with the length
+	algID := lengthPrefixed([]byte(alg))
+	ptyUInfo := lengthPrefixed(apuData)
+	ptyVInfo := lengthPrefixed(apvData)
+
+	// suppPubInfo is the encoded length of the output size in bits
+	supPubInfo := make([]byte, 4)
+	binary.BigEndian.PutUint32(supPubInfo, uint32(size)*8)
+
+	if !priv.PublicKey.Curve.IsOnCurve(pub.X, pub.Y) {
+		panic("public key not on same curve as private key")
+	}
+
+	z, _ := priv.Curve.ScalarMult(pub.X, pub.Y, priv.D.Bytes())
+	zBytes := z.Bytes()
+
+	// Note that calling z.Bytes() on a big.Int may strip leading zero bytes from
+	// the returned byte array. This can lead to a problem where zBytes will be
+	// shorter than expected which breaks the key derivation. Therefore we must pad
+	// to the full length of the expected coordinate here before calling the KDF.
+	octSize := dSize(priv.Curve)
+	if len(zBytes) != octSize {
+		zBytes = append(bytes.Repeat([]byte{0}, octSize-len(zBytes)), zBytes...)
+	}
+
+	reader := NewConcatKDF(crypto.SHA256, zBytes, algID, ptyUInfo, ptyVInfo, supPubInfo, []byte{})
+	key := make([]byte, size)
+
+	// Read on the KDF will never fail
+	_, _ = reader.Read(key)
+
+	return key
+}
+
+// dSize returns the size in octets for a coordinate on a elliptic curve.
+func dSize(curve elliptic.Curve) int {
+	order := curve.Params().P
+	bitLen := order.BitLen()
+	size := bitLen / 8
+	if bitLen%8 != 0 {
+		size++
+	}
+	return size
+}
+
+func lengthPrefixed(data []byte) []byte {
+	out := make([]byte, len(data)+4)
+	binary.BigEndian.PutUint32(out, uint32(len(data)))
+	copy(out[4:], data)
+	return out
+}