Implement SupportsPBKDF2 (#207)

* implement SupportsPBKDF2

* add docs

Author: qmuntal

Diff for: pbkdf2.go

@@ -7,8 +7,38 @@ import "C"
 import (
 	"errors"
 	"hash"
+	"sync"
+	"unsafe"
 )
 
+// SupportsPBKDF2 reports whether the current OpenSSL version supports PBKDF2.
+func SupportsPBKDF2() bool {
+	switch vMajor {
+	case 1:
+		return true
+	case 3:
+		_, err := fetchPBKDF2()
+		return err == nil
+	default:
+		panic(errUnsupportedVersion())
+	}
+}
+
+// fetchPBKDF2 fetches the PBKDF2 algorithm.
+// It is safe to call this function concurrently.
+// The returned EVP_KDF_PTR shouldn't be freed.
+var fetchPBKDF2 = sync.OnceValues(func() (C.GO_EVP_KDF_PTR, error) {
+	checkMajorVersion(3)
+
+	name := C.CString("PBKDF2")
+	kdf := C.go_openssl_EVP_KDF_fetch(nil, name, nil)
+	C.free(unsafe.Pointer(name))
+	if kdf == nil {
+		return nil, newOpenSSLError("EVP_KDF_fetch")
+	}
+	return kdf, nil
+})
+
 func PBKDF2(password, salt []byte, iter, keyLen int, fh func() hash.Hash) ([]byte, error) {
 	h, err := hashFuncHash(fh)
 	if err != nil {

Diff for: pbkdf2_test.go

@@ -138,6 +138,9 @@ var sha256TestVectors = []testVector{
 }
 
 func testHash(t *testing.T, h func() hash.Hash, hashName string, vectors []testVector) {
+	if !openssl.SupportsPBKDF2() {
+		t.Skip("PBKDF2 is not supported")
+	}
 	for i, v := range vectors {
 		o, err := openssl.PBKDF2([]byte(v.password), []byte(v.salt), v.iter, len(v.output), h)
 		if err != nil {
@@ -150,15 +153,18 @@ func testHash(t *testing.T, h func() hash.Hash, hashName string, vectors []testV
 	}
 }
 
-func TestWithHMACSHA1(t *testing.T) {
+func TestPBKDF2WithHMACSHA1(t *testing.T) {
 	testHash(t, openssl.NewSHA1, "SHA1", sha1TestVectors)
 }
 
-func TestWithHMACSHA256(t *testing.T) {
+func TestPBKDF2WithHMACSHA256(t *testing.T) {
 	testHash(t, openssl.NewSHA256, "SHA256", sha256TestVectors)
 }
 
-func TestWithUnsupportedHash(t *testing.T) {
+func TestPBKDF2WithUnsupportedHash(t *testing.T) {
+	if !openssl.SupportsPBKDF2() {
+		t.Skip("PBKDF2 is not supported")
+	}
 	// Test that PBKDF2 returns an error for unsupported hashes instead of panicking.
 	_, err := openssl.PBKDF2([]byte{1, 2}, []byte{3, 4}, 0, 2, newStubHash)
 	if err == nil {
@@ -179,10 +185,10 @@ func benchmark(b *testing.B, h func() hash.Hash) {
 	sink += password[0]
 }
 
-func BenchmarkHMACSHA1(b *testing.B) {
+func BenchmarkPBKDF2HMACSHA1(b *testing.B) {
 	benchmark(b, sha1.New)
 }
 
-func BenchmarkHMACSHA256(b *testing.B) {
+func BenchmarkPBKDF2HMACSHA256(b *testing.B) {
 	benchmark(b, sha256.New)
 }