lib: put rand functions in rand.go

1 files changed, 47 insertions, 0 deletions

diff --git a/lib/rand.go b/lib/rand.go
new file mode 100644
index 0000000..03fd651
--- /dev/null
+++ b/lib/rand.go
@@ -0,0 +1,47 @@
+// Copyright © 2020 rsiddharth <s@ricketyspace.net>
+// SPDX-License-Identifier: ISC
+
+package lib
+
+import (
+	"crypto/rand"
+	"math/big"
+)
+
+// Return a random number from range [min, max]
+func RandomInt(min, max int64) int64 {
+	if min >= max {
+		panic("RandomInt: min cannot be >= max!")
+	}
+
+	var rn *big.Int
+	var err error
+	for {
+		rn, err = rand.Int(rand.Reader, big.NewInt(max+1))
+		if err != nil {
+			panic(err)
+		}
+		if rn.Int64() >= min {
+			return rn.Int64()
+		}
+	}
+}
+
+func RandomKey(size int) ([]byte, error) {
+	k := make([]byte, size)
+	_, err := rand.Read(k)
+	if err != nil {
+		return []byte{}, err
+	}
+	return k, nil
+}
+
+// Randomly generates `min` to `max` bytes.
+func randomBytes(min, max int64) []byte {
+	bs := make([]byte, RandomInt(min, max))
+	_, err := rand.Read(bs)
+	if err != nil {
+		panic(err)
+	}
+	return bs
+}