Add examples.

EXECUTABLE EXAMPLES

Man is that cool.

README.md

@@ -4,31 +4,4 @@ rfc6979
 A Go implementation of [RFC 6979](https://tools.ietf.org/html/rfc6979)'s
 deterministic DSA/ECDSA signature scheme.
 
-``` go
+For documentation, check [godoc](http://godoc.org/github.com/codahale/rfc6979).
-package main
-
-import (
-	"crypto/ecdsa"
-	"crypto/elliptic"
-	"crypto/rand"
-	"crypto/sha512"
-	"fmt"
-	"github.com/codahale/rfc6979"
-)
-
-func main() {
-	// Generate a key pair.
-	// You need a high-quality PRNG for this.
-	k, _ := ecdsa.GenerateKey(elliptic.P521(), rand.Reader)
-
-	// Hash a message.
-	alg := sha512.New()
-	alg.Write([]byte("I am a potato."))
-	hash := alg.Sum(nil)
-
-	// Sign the message. You don't need a PRNG for this.
-	r, s, _ := rfc6979.SignECDSA(k, hash, sha512.New)
-	fmt.Printf("Signature: %X%X", r, s)
-}
-
-```

example_test.go

@@ -0,0 +1,76 @@
+package rfc6979
+
+import (
+	"crypto/ecdsa"
+	"crypto/sha512"
+	"crypto/rand"
+	"crypto/elliptic"
+	"crypto/dsa"
+	"crypto/sha1"
+	"fmt"
+)
+
+// Generates a 521-bit ECDSA key, uses SHA-512 to sign a message, then verifies
+// it.
+func ExampleSignECDSA() {
+	// Generate a key pair.
+	// You need a high-quality PRNG for this.
+	k, err := ecdsa.GenerateKey(elliptic.P521(), rand.Reader)
+
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+
+	// Hash a message.
+	alg := sha512.New()
+	alg.Write([]byte("I am a potato."))
+	hash := alg.Sum(nil)
+
+	// Sign the message. You don't need a PRNG for this.
+	r, s, err := SignECDSA(k, hash, sha512.New)
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+
+	if !ecdsa.Verify(&k.PublicKey, hash, r, s) {
+		fmt.Println("Invalid signature!")
+	}
+
+	// Output:
+}
+
+// Generates a 1024-bit DSA key, uses SHA-1 to sign a message, then verifies it.
+func ExampleSignDSA() {
+	// Here I'm generating some DSA params, but you should really pre-generate
+	// these and re-use them, since this takes a long time and isn't necessary.
+	k := new(dsa.PrivateKey)
+	dsa.GenerateParameters(&k.Parameters, rand.Reader, dsa.L1024N160)
+
+	// Generate a key pair.
+	// You need a high-quality PRNG for this.
+	err := dsa.GenerateKey(k, rand.Reader)
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+
+	// Hash a message.
+	alg := sha1.New()
+	alg.Write([]byte("I am a potato."))
+	hash := alg.Sum(nil)
+
+	// Sign the message. You don't need a PRNG for this.
+	r, s, err := SignDSA(k, hash, sha1.New)
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+
+	if !dsa.Verify(&k.PublicKey, hash, r, s) {
+		fmt.Println("Invalid signature!")
+	}
+
+	// Output:
+}