// ====================
// 1.  If there is no receipt, verification fails.
CFURLRef receiptURL = CFBundleCopyResourceURL(CFBundleGetMainBundle(), CFSTR("receipt"), NULL, CFSTR("_MASReceipt"));
if(NULL == receiptURL)
	exit(173);

// ====================
// 2.  If the receipt is not properly signed by Apple, verification fails.
CFDictionaryRef receiptDictionary = CreateDictionaryForAppStoreReceipt(receiptURL);
if(NULL == receiptDictionary)
	exit(173);

// ====================
// 3.  If the bundle identifier in the receipt does not match the value for CFBundleIdentifier in the Info.plist file, verification fails.
CFStringRef receiptBundleID = CFDictionaryGetValue(receiptDictionary, CFSTR(kReceiptBundleIdentifer));
if(NULL == receiptBundleID)
	exit(173);

CFStringRef bundleID = CFBundleGetValueForInfoDictionaryKey(CFBundleGetMainBundle(), CFSTR("CFBundleIdentifier"));
if(kCFCompareEqualTo != CFStringCompare(receiptBundleID, bundleID, (CFOptionFlags)0))
	exit(173);

// ====================
// 4.  If the version identifier string in the receipt does not match the value for CFBundleShortVersionString in the Info.plist file, verification fails.
CFStringRef receiptVersionID = CFDictionaryGetValue(receiptDictionary, CFSTR(kReceiptVersion));
if(NULL == receiptVersionID)
	exit(173);

CFStringRef bundleVersionID = CFBundleGetValueForInfoDictionaryKey(CFBundleGetMainBundle(), CFSTR("CFBundleShortVersionString"));
if(kCFCompareEqualTo != CFStringCompare(receiptVersionID, bundleVersionID, (CFOptionFlags)0))
	exit(173);

// ====================
// 5.  Concatenate the bytes of the computer’s GUID, the opaque value (the attribute of type 4), and the bundle identifier from the receipt. Compute the SHA-1 hash. If the result does not match the hash in the receipt, verification fails.
CFDataRef guid = CopyMachineGUID();
CFDataRef receiptOpaqueValue = CFDictionaryGetValue(receiptDictionary, CFSTR(kReceiptOpaqueValue));
CFDataRef receiptBundleIDData = CFStringCreateExternalRepresentation(kCFAllocatorDefault, receiptBundleID, kCFStringEncodingUTF8, (UInt8)0);

if(NULL == guid || NULL == receiptOpaqueValue || NULL == receiptBundleIDData)
	exit(173);

CC_SHA1_CTX sha1;
CC_SHA1_Init(&sha1);

CC_SHA1_Update(&sha1, CFDataGetBytePtr(guid), (CC_LONG)CFDataGetLength(guid));
CC_SHA1_Update(&sha1, CFDataGetBytePtr(receiptOpaqueValue), (CC_LONG)CFDataGetLength(receiptOpaqueValue));
CC_SHA1_Update(&sha1, CFDataGetBytePtr(receiptBundleIDData), (CC_LONG)CFDataGetLength(receiptBundleIDData));

unsigned char sha1Digest [CC_SHA1_DIGEST_LENGTH];
CC_SHA1_Final(sha1Digest, &sha1);

CFDataRef computedSHA1Hash = CFDataCreate(kCFAllocatorDefault, sha1Digest, (CFIndex)CC_SHA1_DIGEST_LENGTH);

CFDataRef receiptSHA1Hash = CFDictionaryGetValue(receiptDictionary, CFSTR(kReceiptHash));
if(kCFCompareEqualTo != CFEqual(computedSHA1Hash, receiptSHA1Hash))
	exit(173);

// If all of the above checks pass, verification passes.
CFRelease(computedSHA1Hash), computedSHA1Hash = NULL;
CFRelease(receiptBundleIDData), receiptBundleIDData = NULL;
CFRelease(guid), guid = NULL;
CFRelease(receiptDictionary), receiptDictionary = NULL;