QCE Digital Solutions Unit 4 Definitions Worksheet: Digital Methods for Exchanging Data (Modules 17–88)
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Key terms
Write what each term means, in your own words.
1
Gronsfeld cipher
2
one-time pad
3
block cipher
4
DES
5
Triple DES
6
Blowfish
7
Twofish
8
compress then encrypt
9
jitter
10
guaranteed delivery
Answer Key
QCE Digital Solutions Unit 4 · Modules 17–88 · Student wording will vary for definitions
1Gronsfeld cipher — A Vigenere variant whose key is a string of digits 0-9, like 31415. Each digit is the shift for one letter, and the key repeats along the message.
2one-time pad — Encryption using a truly random key as long as the message, used only once. Never reused, it is unbreakable in theory, but the pad must be shared securely.
3block cipher — Encrypts data in fixed-size blocks (e.g. 128 bits) using a key, scrambling each block in rounds. A longer key means more possible keys, so brute force takes longer.
4DES — Data Encryption Standard: an early symmetric block cipher using 64-bit blocks and a 56-bit key. Now insecure because modern computers can brute-force its small key.
5Triple DES — Applies DES three times (encrypt, decrypt, encrypt) with two or three keys to lengthen the effective key and strengthen DES. It is slower than AES.
6Blowfish — A fast symmetric block cipher with a variable-length key (up to 448 bits) and 64-bit blocks. It is free for anyone to use, as it is in the public domain.
7Twofish — A symmetric block cipher and Blowfish's successor. It encrypts 128-bit blocks with keys up to 256 bits and was a finalist in the competition that chose AES.
8compress then encrypt — Compress first, then encrypt, and hash to check integrity. Encrypted data looks random so it cannot be compressed. On receiving, reverse the order: decrypt, then decompress.
9jitter — The variation in latency between packets, so they arrive at uneven intervals. Measured in milliseconds, it disrupts voice and video unless a jitter buffer smooths it.
10guaranteed delivery — Every packet is confirmed as received (acknowledged). Missing or damaged packets are resent so no data is lost, but waiting and resending adds extra delay.