diff --git a/Base32.xcodeproj/project.pbxproj b/Base32.xcodeproj/project.pbxproj
index b3c22ea..5bb98a2 100644
--- a/Base32.xcodeproj/project.pbxproj
+++ b/Base32.xcodeproj/project.pbxproj
@@ -9,6 +9,8 @@
 /* Begin PBXBuildFile section */
 		6C10E90F1A753A6C006EED90 /* Base32.h in Headers */ = {isa = PBXBuildFile; fileRef = 6CA0A79D1A74E80600AC539F /* Base32.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		6C10E91A1A754346006EED90 /* TTTDataTransformer.m in Sources */ = {isa = PBXBuildFile; fileRef = 6C10E9141A7540B5006EED90 /* TTTDataTransformer.m */; };
+		6C122F7D1A85E52C004FD458 /* StringExtension.swift in Sources */ = {isa = PBXBuildFile; fileRef = 6C122F7C1A85E52C004FD458 /* StringExtension.swift */; };
+		6C122F7E1A85E52C004FD458 /* StringExtension.swift in Sources */ = {isa = PBXBuildFile; fileRef = 6C122F7C1A85E52C004FD458 /* StringExtension.swift */; };
 		6CA0A79E1A74E80600AC539F /* Base32.h in Headers */ = {isa = PBXBuildFile; fileRef = 6CA0A79D1A74E80600AC539F /* Base32.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		6CA0A7A41A74E80600AC539F /* Base32.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 6CA0A7981A74E80600AC539F /* Base32.framework */; };
 		6CA0A7AB1A74E80600AC539F /* Base32Tests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 6CA0A7AA1A74E80600AC539F /* Base32Tests.swift */; };
@@ -42,6 +44,7 @@
 		6C10E9121A7540B4006EED90 /* SecEncodeTransformTests-Bridging-Header.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = "SecEncodeTransformTests-Bridging-Header.h"; sourceTree = "<group>"; };
 		6C10E9131A7540B5006EED90 /* TTTDataTransformer.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = TTTDataTransformer.h; sourceTree = "<group>"; };
 		6C10E9141A7540B5006EED90 /* TTTDataTransformer.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = TTTDataTransformer.m; sourceTree = "<group>"; };
+		6C122F7C1A85E52C004FD458 /* StringExtension.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = StringExtension.swift; sourceTree = "<group>"; };
 		6CA0A7981A74E80600AC539F /* Base32.framework */ = {isa = PBXFileReference; explicitFileType = wrapper.framework; includeInIndex = 0; path = Base32.framework; sourceTree = BUILT_PRODUCTS_DIR; };
 		6CA0A79C1A74E80600AC539F /* Info.plist */ = {isa = PBXFileReference; lastKnownFileType = text.plist.xml; path = Info.plist; sourceTree = "<group>"; };
 		6CA0A79D1A74E80600AC539F /* Base32.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = Base32.h; sourceTree = "<group>"; };
@@ -152,6 +155,7 @@
 			children = (
 				6CA0A79D1A74E80600AC539F /* Base32.h */,
 				6CA0A7EF1A74ECEE00AC539F /* Base32.swift */,
+				6C122F7C1A85E52C004FD458 /* StringExtension.swift */,
 				6CA0A79B1A74E80600AC539F /* Supporting Files */,
 			);
 			path = Base32;
@@ -479,6 +483,7 @@
 			isa = PBXSourcesBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				6C122F7D1A85E52C004FD458 /* StringExtension.swift in Sources */,
 				6CA0A7F01A74ECEE00AC539F /* Base32.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
@@ -495,6 +500,7 @@
 			isa = PBXSourcesBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				6C122F7E1A85E52C004FD458 /* StringExtension.swift in Sources */,
 				6CA0A7F11A74ECEE00AC539F /* Base32.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
diff --git a/Base32/Base32.swift b/Base32/Base32.swift
index cab2b73..1aa4447 100644
--- a/Base32/Base32.swift
+++ b/Base32/Base32.swift
@@ -106,8 +106,8 @@ extension NSData {
         return base32Encode(self)
     }
     
-    public var base32EncodedData: NSData? {
-        return base32EncodedString.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false)
+    public var base32EncodedData: NSData {
+        return base32EncodedString.dataUsingUTF8StringEncoding
     }
     
     public var base32DecodedData: NSData? {
@@ -123,8 +123,8 @@ extension NSData {
         return base32HexEncode(self)
     }
     
-    public var base32HexEncodedData: NSData? {
-        return base32HexEncodedString.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false)
+    public var base32HexEncodedData: NSData {
+        return base32HexEncodedString.dataUsingUTF8StringEncoding
     }
     
     public var base32HexDecodedData: NSData? {
diff --git a/Base32/StringExtension.swift b/Base32/StringExtension.swift
new file mode 100644
index 0000000..02e6632
--- /dev/null
+++ b/Base32/StringExtension.swift
@@ -0,0 +1,29 @@
+//
+//  StringExtension.swift
+//  Base32
+//
+//  Created by 野村 憲男 on 2/7/15.
+//  Copyright (c) 2015 Norio Nomura. All rights reserved.
+//
+
+import Foundation
+
+// MARK: - private
+
+extension String {
+    /// NSData never nil
+    internal var dataUsingUTF8StringEncoding: NSData {
+        let length = nulTerminatedUTF8.count - 1
+        return nulTerminatedUTF8.withUnsafeBufferPointer {
+            return NSData(bytes: $0.baseAddress, length: length)
+        }
+    }
+    
+    /// Array<UInt8>
+    internal var arrayUsingUTF8StringEncoding: [UInt8] {
+        let length = nulTerminatedUTF8.count - 1
+        return nulTerminatedUTF8.withUnsafeBufferPointer {
+            return Array(UnsafeBufferPointer(start: $0.baseAddress, count: length))
+        }
+    }
+}
diff --git a/Base32Tests/Base32Tests.swift b/Base32Tests/Base32Tests.swift
index b0085d4..c47553a 100644
--- a/Base32Tests/Base32Tests.swift
+++ b/Base32Tests/Base32Tests.swift
@@ -114,10 +114,10 @@ class Base32Tests: XCTestCase {
                 for (test, expect, expectHex) in dataVectors {
                     let result = test.base32EncodedData
                     let resultHex = test.base32HexEncodedData
-                    XCTAssertEqual(result!, expect, "\(test).base32EncodedData")
-                    XCTAssertEqual(resultHex!, expectHex, "\(test).base32HexEncodedData")
-                    let decoded = result!.base32DecodedData
-                    let decodedHex = resultHex!.base32HexDecodedData
+                    XCTAssertEqual(result, expect, "\(test).base32EncodedData")
+                    XCTAssertEqual(resultHex, expectHex, "\(test).base32HexEncodedData")
+                    let decoded = result.base32DecodedData
+                    let decodedHex = resultHex.base32HexDecodedData
                     XCTAssertEqual(decoded!, test, "\(result).base32DecodedData")
                     XCTAssertEqual(decodedHex!, test, "\(resultHex).base32HexDecodedData")
                 }