Add dep

vendor/github.com/Rhymen/go-whatsapp/crypto/hkdf/hkdf.go

@@ -0,0 +1,52 @@
+/*
+HKDF is a simple key derivation function (KDF) based on
+a hash-based message authentication code (HMAC). It was initially proposed by its authors as a building block in
+various protocols and applications, as well as to discourage the proliferation of multiple KDF mechanisms.
+The main approach HKDF follows is the "extract-then-expand" paradigm, where the KDF logically consists of two modules:
+the first stage takes the input keying material and "extracts" from it a fixed-length pseudorandom key, and then the
+second stage "expands" this key into several additional pseudorandom keys (the output of the KDF).
+*/
+package hkdf
+
+import (
+	"crypto/hmac"
+	"crypto/sha256"
+	"fmt"
+	"golang.org/x/crypto/hkdf"
+	"io"
+)
+
+/*
+Expand expands a given key with the HKDF algorithm.
+*/
+func Expand(key []byte, length int, info string) ([]byte, error) {
+	if info == "" {
+		keyBlock := hmac.New(sha256.New, key)
+		var out, last []byte
+
+		var blockIndex byte = 1
+		for i := 0; len(out) < length; i++ {
+			keyBlock.Reset()
+			//keyBlock.Write(append(append(last, []byte(info)...), blockIndex))
+			keyBlock.Write(last)
+			keyBlock.Write([]byte(info))
+			keyBlock.Write([]byte{blockIndex})
+			last = keyBlock.Sum(nil)
+			blockIndex += 1
+			out = append(out, last...)
+		}
+		return out[:length], nil
+	} else {
+		h := hkdf.New(sha256.New, key, nil, []byte(info))
+		out := make([]byte, length)
+		n, err := io.ReadAtLeast(h, out, length)
+		if err != nil {
+			return nil, err
+		}
+		if n != length {
+			return nil, fmt.Errorf("new key to short")
+		}
+
+		return out[:length], nil
+	}
+}