trivial: add PasswordHash and RandomBytes

trivial/password.go

+package trivial
+
+import (
+        "crypto/rand"
+        "crypto/sha512"
+        "encoding/base64"
+        "fmt"
+        "io"
+        "launchpad.net/juju-core/thirdparty/pbkdf2"
+)
+
+var salt = []byte{0x75, 0x82, 0x81, 0xca}
+
+// RandomBytes returns n random bytes.
+func RandomBytes(n int) ([]byte, error) {
+        buf := make([]byte, n)
+        _, err := io.ReadFull(rand.Reader, buf)
+        if err != nil {
+                return nil, fmt.Errorf("cannot read random bytes: %v", err)
+        }
+        return buf, nil
+}
+
+// PasswordHash returns base64-encoded one-way hash of the provided salt
+// and password that is computationally hard to crack by iterating
+// through possible passwords.
+func PasswordHash(password string) string {
+        // Generate 18 byte passwords because we know that MongoDB
+        // uses the MD5 sum of the password anyway, so there's
+        // no point in using more bytes. (18 so we don't get base 64
+        // padding characters).
+        h := pbkdf2.Key([]byte(password), salt, 8192, 18, sha512.New)
+        return base64.StdEncoding.EncodeToString(h)
+}