Merge branch 'jonah/checkFP' into 'agile/EphemeralReception'

Jonah/check fp

See merge request elixxir/crypto!254

fingerprint/fingerprint.go

@@ -8,6 +8,7 @@
 package fingerprint
 
 import (
+	"bytes"
 	"crypto"
 	"github.com/pkg/errors"
 	"gitlab.com/xx_network/primitives/id"
@@ -34,3 +35,12 @@ func IdentityFP(encryptedMessagePayload []byte, recipientId *id.ID) ([]byte, err
 	}
 	return b2b.Sum(nil)[:identityFpSizeBytes], nil
 }
+
+// Check if a received fingerprint is correct based on message payload and ID
+func CheckIdentityFP(receivedFP, encryptedMessagePayload []byte, recipientId *id.ID) (bool, error) {
+	identityFP, err := IdentityFP(encryptedMessagePayload, recipientId)
+	if err != nil {
+		return false, err
+	}
+	return bytes.Compare(identityFP, receivedFP) == 0, nil
+}

fingerprint/fingerprint_test.go

@@ -54,3 +54,19 @@ func TestIdentityFP(t *testing.T) {
 		t.Logf("\n\tID1 [%+v]\n\tID2 [%+v]\n\tID3 [%+v]\n\tID4 [%+v]\n\tID5 [%+v]\n", fp1, fp2, fp3, fp4, fp5)
 	}
 }
+
+func TestCheckIdentityFP(t *testing.T) {
+	message1 := []byte("I'm an encrypted message!")
+	user1 := id.NewIdFromString("zezima", id.User, t)
+
+	// Check that two fingerprints created from the same data are identical
+	fp1, err := IdentityFP(message1, user1)
+	if err != nil {
+		t.Errorf("Failed to create identity fingerprint 1: %+v", err)
+	}
+
+	ok, err := CheckIdentityFP(fp1, message1, user1)
+	if err != nil || !ok {
+		t.Errorf("Should have gotten ok from CheckIdentityFP.  Instead got (%+v, %+v)", ok, err)
+	}
+}