checksum

I'm building a system which needs to be able to find if blobs of bytes have been updated . Rather than storing the whole blob (they can be up to 5MBs), I'm thinking I should compute a checksum of it, store this and compute the same checksum a little bit later, to see whether the blog has been updated. The goal is to minimize the following (in that order) : size of the checksum time to compute likeliness of collisions (2 identical checksums happening even if the content has been modified). It is acceptable for our system to have collision not more than 1/1,000,000. The concern is not security,

I was trying to implement the Luhn Formula in Python, here is my code: import sys def luhn_check(number): if number.isdigit(): last_digit = int(str(number)[-1]) reverse_sequence = list(int(d) for d in str(int(number[-2::-1]))) for i in range(0, len(reverse_sequence), 2): reverse_sequence[i] *= 2 for i in range(len(reverse_sequence)): if reverse_sequence[i] > 9: reverse_sequence[i] -= 9 sum_of_digits = 0 for i in range(len(reverse_sequence)): sum_of_digits += reverse_sequence[i] result = divmod(sum_of_digits, 10) if result == last_digit: print("[VALID] %s" % number) else: print("[INVALID] %s" %

This is almost certainly a very silly question, but for some reason I'm having trouble with internet checksum calculations. All of the algorithms basically look something like this: WORD chksm(WORD *startpos, WORD checklen){ ulong sum = 0; WORD answer = 0; while (checklen > 1) { sum += *startpos++; checklen -= 2; } if (checklen == 1) { *(BYTE *)(&answer) = *(BYTE *)startpos; sum += answer; } sum = (sum >> 16) + (sum & 0xffff); sum += (sum >> 16); answer = ~sum; return answer;} I'm clear on everything except for the line: sum += (sum >> 16); It looks like the line immediately before it adds the

I want to integrate Paytm SDK in my app. I have MerchantId and Merchant key . But i don't have those Urls. How to generate those URLS? I integrated PayTM sdk into swift application and its working fine . The issue where i got stuck about 15 days is the URL Generation : checkSumGenerationURL and checkSumValidationURL . Earlier i was using PayTM provided url but due to this it gets failed every time trying to payment . so here is the final solution : I sit with my server team and then decided to handle it in our own server then after try it . It works great . So here is final set of parameters

I'm working on creating the MD5 Checksum for large video files. I'm currently using the code: extension NSData { func MD5() -> NSString { let digestLength = Int(CC_MD5_DIGEST_LENGTH) let md5Buffer = UnsafeMutablePointer<CUnsignedChar>.allocate(capacity: digestLength) CC_MD5(bytes, CC_LONG(length), md5Buffer) let output = NSMutableString(capacity: Int(CC_MD5_DIGEST_LENGTH * 2)) for i in 0..<digestLength { output.appendFormat("%02x", md5Buffer[i]) } return NSString(format: output) } } But that creates a memory buffer, and for large video files would not be ideal. Is there a way in Swift to

Is there a way to get the MD5 or SHA-1 checksum/hash of a file on disk in Qt? For example, I have the file path and I might need to verify that the contents of that file matches a certain hash value. cmannett85 Open the file with QFile , and call readAll() to pull it's contents into a QByteArray . Then use that for the QCryptographicHash::hash(const QByteArray& data, Algorithm method) call. In Qt5 you can use addData() : // Returns empty QByteArray() on failure. QByteArray fileChecksum(const QString &fileName, QCryptographicHash::Algorithm hashAlgorithm) { QFile f(fileName); if (f.open(QFile: