Question 1

What is a checksum and why is it used?

Accepted Answer

A checksum is a small-sized value derived from a block of data using a mathematical algorithm. It is used to detect errors in data transmission or storage. If the checksum of received data matches the expected checksum, the data is likely intact. Common checksums include CRC-16, CRC-32, and Adler-32.

Question 2

What is the difference between CRC-16, CRC-24, and CRC-32?

Accepted Answer

CRC-16 produces a 16-bit (2-byte) checksum, CRC-24 a 24-bit (3-byte) value, and CRC-32 a 32-bit (4-byte) value. Higher bit-width CRCs have a lower collision probability and detect a wider range of errors. CRC-32 is the most widely used — it is used in Ethernet, ZIP files, and PNG images. CRC-16 is common in serial protocols and storage devices.

Question 3

What is Adler-32 and how does it differ from CRC-32?

Accepted Answer

Adler-32 is a fast checksum algorithm used in the zlib compression library. Unlike CRC-32, which uses a polynomial division, Adler-32 uses a pair of running sums over the data bytes. It is faster to compute than CRC-32 but has slightly weaker error detection for small messages.

Question 4

What is the Luhn algorithm?

Accepted Answer

The Luhn algorithm (mod-10) is a simple checksum formula used to validate credit card numbers, IMEI numbers, and other identification numbers. It works by doubling every second digit from the right, summing all digits, and checking whether the total is divisible by 10. A valid number passes the Luhn check; the tool also computes the check digit for a given number prefix.

Question 5

What does the Hex input mode do?

Accepted Answer

In Hex mode, the input is interpreted as a hexadecimal byte string (e.g., 'DEADBEEF' or '48 65 6C 6C 6F'). Spaces are ignored. This is useful when you have raw binary data represented as hex and want to compute checksums over the actual byte values rather than the ASCII characters of the hex string.

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