What does Blockcypher do

Block ciphers / block ciphers

A block cipher is an encryption method and is part of symmetric cryptography. In the case of block ciphers or block ciphers, the data are encrypted individually and one after the other in blocks of a specified size. If the data does not fill a whole block, then the block will be filled with what is known as "padding" at the end.

Block length

With block ciphers, the block length, i.e. the length of the bit sequence that is encrypted, should be at least 128 bits. A block length of only 64 bits would correspond to 8 letters in the UTF-8 character set, which can easily be repeated in the respective sequence.

Modes of operation

There are various options for block-by-block encryption. The procedure is defined in the so-called operating modes or operating modes.

  • ECB - Electronic Code Book Mode
  • CBC - Cipher Block Chaining Mode
  • CTR - Counter Mode
  • OFB - Output Feedback Mode
  • CFB - Cipher Feedback Mode

ECB - Electronic Codebook

With the Electronic Codebook (ECB), each block is encrypted with the same key. The problem here is that if you encrypt the same thing twice, you get the same result twice. This is bad because an attacker can use pattern recognition to infer the content.
The problem can be solved by working with a sufficiently large block length. For example, let's take a block length of 32 bits. If you always encrypt 4 bytes in a row, then that's just 4 characters according to Unicode (8 bits).
If the attacker records enough data, it is very likely that encrypted blocks will repeat. This is not a good thing, because if the attacker can assign part of the ciphertext to plaintext, then he may be able to get other parts of the ciphertext as well.

CBC - Cipherblock Chaining

Cipherblock Chaining (CBC) is another option for block-wise encryption. The previous encrypted block is included in the next block. So the block changes from block to block, even if it always says the same thing. But that's not ideal either.

CTR - Counter mode

CTR works in a similar way to CBC. With CTR, the start value is initialized with a so-called nonce (number used only once). There is a risk that if a nonce is used a second time, the encryption can be canceled by XORing both messages.

Overview: known block ciphers

  • OF
  • Camellia
  • RC2
  • 3DES
  • RC6
  • AES
  • Blowfish
  • Serpent
  • Twofish
  • CAST
  • MARS

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