diff --git a/crypto/crypto.go b/crypto/crypto.go
index b3a8d730b..272050106 100644
--- a/crypto/crypto.go
+++ b/crypto/crypto.go
@@ -172,10 +172,10 @@ func GenerateKey() (*ecdsa.PrivateKey, error) {
 }
 
 func ValidateSignatureValues(v byte, r, s *big.Int) bool {
-	vint := uint32(v)
-	if r.Cmp(common.Big0) == 0 || s.Cmp(common.Big0) == 0 {
+	if r.Cmp(common.Big1) < 0 || s.Cmp(common.Big1) < 0 {
 		return false
 	}
+	vint := uint32(v)
 	if r.Cmp(secp256k1n) < 0 && s.Cmp(secp256k1n) < 0 && (vint == 27 || vint == 28) {
 		return true
 	} else {
@@ -302,17 +302,6 @@ func aesCBCDecrypt(key, cipherText, iv []byte) ([]byte, error) {
 }
 
 // From https://leanpub.com/gocrypto/read#leanpub-auto-block-cipher-modes
-func PKCS7Pad(in []byte) []byte {
-	padding := 16 - (len(in) % 16)
-	if padding == 0 {
-		padding = 16
-	}
-	for i := 0; i < padding; i++ {
-		in = append(in, byte(padding))
-	}
-	return in
-}
-
 func PKCS7Unpad(in []byte) []byte {
 	if len(in) == 0 {
 		return nil
diff --git a/crypto/crypto_test.go b/crypto/crypto_test.go
index b891f41a9..fdd9c1ee8 100644
--- a/crypto/crypto_test.go
+++ b/crypto/crypto_test.go
@@ -18,8 +18,12 @@ package crypto
 
 import (
 	"bytes"
+	"crypto/ecdsa"
 	"encoding/hex"
 	"fmt"
+	"io/ioutil"
+	"math/big"
+	"os"
 	"testing"
 	"time"
 
@@ -27,10 +31,12 @@ import (
 	"github.com/ethereum/go-ethereum/crypto/secp256k1"
 )
 
+var testAddrHex = "970e8128ab834e8eac17ab8e3812f010678cf791"
+var testPrivHex = "289c2857d4598e37fb9647507e47a309d6133539bf21a8b9cb6df88fd5232032"
+
 // These tests are sanity checks.
 // They should ensure that we don't e.g. use Sha3-224 instead of Sha3-256
 // and that the sha3 library uses keccak-f permutation.
-
 func TestSha3(t *testing.T) {
 	msg := []byte("abc")
 	exp, _ := hex.DecodeString("4e03657aea45a94fc7d47ba826c8d667c0d1e6e33a64a036ec44f58fa12d6c45")
@@ -55,13 +61,6 @@ func TestRipemd160(t *testing.T) {
 	checkhash(t, "Ripemd160", Ripemd160, msg, exp)
 }
 
-func checkhash(t *testing.T, name string, f func([]byte) []byte, msg, exp []byte) {
-	sum := f(msg)
-	if bytes.Compare(exp, sum) != 0 {
-		t.Errorf("hash %s returned wrong result.\ngot:  %x\nwant: %x", name, sum, exp)
-	}
-}
-
 func BenchmarkSha3(b *testing.B) {
 	a := []byte("hello world")
 	amount := 1000000
@@ -74,13 +73,41 @@ func BenchmarkSha3(b *testing.B) {
 }
 
 func Test0Key(t *testing.T) {
-	t.Skip()
-	key := common.Hex2Bytes("1111111111111111111111111111111111111111111111111111111111111111")
+	key := common.Hex2Bytes("0000000000000000000000000000000000000000000000000000000000000000")
+	_, err := secp256k1.GeneratePubKey(key)
+	if err == nil {
+		t.Errorf("expected error due to zero privkey")
+	}
+}
+
+func TestSign(t *testing.T) {
+	key, _ := HexToECDSA(testPrivHex)
+	addr := common.HexToAddress(testAddrHex)
+
+	msg := Sha3([]byte("foo"))
+	sig, err := Sign(msg, key)
+	if err != nil {
+		t.Errorf("Sign error: %s", err)
+	}
+	recoveredPub, err := Ecrecover(msg, sig)
+	if err != nil {
+		t.Errorf("ECRecover error: %s", err)
+	}
+	recoveredAddr := PubkeyToAddress(*ToECDSAPub(recoveredPub))
+	if addr != recoveredAddr {
+		t.Errorf("Address mismatch: want: %x have: %x", addr, recoveredAddr)
+	}
+
+	// should be equal to SigToPub
+	recoveredPub2, err := SigToPub(msg, sig)
+	if err != nil {
+		t.Errorf("ECRecover error: %s", err)
+	}
+	recoveredAddr2 := PubkeyToAddress(*recoveredPub2)
+	if addr != recoveredAddr2 {
+		t.Errorf("Address mismatch: want: %x have: %x", addr, recoveredAddr2)
+	}
 
-	p, err := secp256k1.GeneratePubKey(key)
-	addr := Sha3(p[1:])[12:]
-	fmt.Printf("%x\n", p)
-	fmt.Printf("%v %x\n", err, addr)
 }
 
 func TestInvalidSign(t *testing.T) {
@@ -94,3 +121,129 @@ func TestInvalidSign(t *testing.T) {
 		t.Errorf("expected sign with hash 33 byte to error")
 	}
 }
+
+func TestNewContractAddress(t *testing.T) {
+	key, _ := HexToECDSA(testPrivHex)
+	addr := common.HexToAddress(testAddrHex)
+	genAddr := PubkeyToAddress(key.PublicKey)
+	// sanity check before using addr to create contract address
+	checkAddr(t, genAddr, addr)
+
+	caddr0 := CreateAddress(addr, 0)
+	caddr1 := CreateAddress(addr, 1)
+	caddr2 := CreateAddress(addr, 2)
+	checkAddr(t, common.HexToAddress("333c3310824b7c685133f2bedb2ca4b8b4df633d"), caddr0)
+	checkAddr(t, common.HexToAddress("8bda78331c916a08481428e4b07c96d3e916d165"), caddr1)
+	checkAddr(t, common.HexToAddress("c9ddedf451bc62ce88bf9292afb13df35b670699"), caddr2)
+}
+
+func TestLoadECDSAFile(t *testing.T) {
+	keyBytes := common.FromHex(testPrivHex)
+	fileName0 := "test_key0"
+	fileName1 := "test_key1"
+	checkKey := func(k *ecdsa.PrivateKey) {
+		checkAddr(t, PubkeyToAddress(k.PublicKey), common.HexToAddress(testAddrHex))
+		loadedKeyBytes := FromECDSA(k)
+		if !bytes.Equal(loadedKeyBytes, keyBytes) {
+			t.Fatalf("private key mismatch: want: %x have: %x", keyBytes, loadedKeyBytes)
+		}
+	}
+
+	ioutil.WriteFile(fileName0, []byte(testPrivHex), 0600)
+	defer os.Remove(fileName0)
+
+	key0, err := LoadECDSA(fileName0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	checkKey(key0)
+
+	// again, this time with SaveECDSA instead of manual save:
+	err = SaveECDSA(fileName1, key0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.Remove(fileName1)
+
+	key1, err := LoadECDSA(fileName1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	checkKey(key1)
+}
+
+func TestValidateSignatureValues(t *testing.T) {
+	check := func(expected bool, v byte, r, s *big.Int) {
+		if ValidateSignatureValues(v, r, s) != expected {
+			t.Errorf("mismatch for v: %d r: %d s: %d want: %v", v, r, s, expected)
+		}
+	}
+	minusOne := big.NewInt(-1)
+	one := common.Big1
+	zero := common.Big0
+	secp256k1nMinus1 := new(big.Int).Sub(secp256k1n, common.Big1)
+
+	// correct v,r,s
+	check(true, 27, one, one)
+	check(true, 28, one, one)
+	// incorrect v, correct r,s,
+	check(false, 30, one, one)
+	check(false, 26, one, one)
+
+	// incorrect v, combinations of incorrect/correct r,s at lower limit
+	check(false, 0, zero, zero)
+	check(false, 0, zero, one)
+	check(false, 0, one, zero)
+	check(false, 0, one, one)
+
+	// correct v for any combination of incorrect r,s
+	check(false, 27, zero, zero)
+	check(false, 27, zero, one)
+	check(false, 27, one, zero)
+
+	check(false, 28, zero, zero)
+	check(false, 28, zero, one)
+	check(false, 28, one, zero)
+
+	// correct sig with max r,s
+	check(true, 27, secp256k1nMinus1, secp256k1nMinus1)
+	// correct v, combinations of incorrect r,s at upper limit
+	check(false, 27, secp256k1n, secp256k1nMinus1)
+	check(false, 27, secp256k1nMinus1, secp256k1n)
+	check(false, 27, secp256k1n, secp256k1n)
+
+	// current callers ensures r,s cannot be negative, but let's test for that too
+	// as crypto package could be used stand-alone
+	check(false, 27, minusOne, one)
+	check(false, 27, one, minusOne)
+}
+
+func checkhash(t *testing.T, name string, f func([]byte) []byte, msg, exp []byte) {
+	sum := f(msg)
+	if bytes.Compare(exp, sum) != 0 {
+		t.Fatalf("hash %s mismatch: want: %x have: %x", name, exp, sum)
+	}
+}
+
+func checkAddr(t *testing.T, addr0, addr1 common.Address) {
+	if addr0 != addr1 {
+		t.Fatalf("address mismatch: want: %x have: %x", addr0, addr1)
+	}
+}
+
+// test to help Python team with integration of libsecp256k1
+// skip but keep it after they are done
+func TestPythonIntegration(t *testing.T) {
+	kh := "289c2857d4598e37fb9647507e47a309d6133539bf21a8b9cb6df88fd5232032"
+	k0, _ := HexToECDSA(kh)
+	k1 := FromECDSA(k0)
+
+	msg0 := Sha3([]byte("foo"))
+	sig0, _ := secp256k1.Sign(msg0, k1)
+
+	msg1 := common.FromHex("00000000000000000000000000000000")
+	sig1, _ := secp256k1.Sign(msg0, k1)
+
+	fmt.Printf("msg: %x, privkey: %x sig: %x\n", msg0, k1, sig0)
+	fmt.Printf("msg: %x, privkey: %x sig: %x\n", msg1, k1, sig1)
+}