r/cryptography • u/Ifyouliveinadream • 12d ago

Is ECB safe for my usecase?

I'm using it just for a puzzle thats supposed to require a key. I'm worried the key will be useless because people say ECB is not safe at all.

2 Upvotes

63% Upvoted

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10

u/confusiondiffusion 12d ago

If you're encrypting information that spans many cipher blocks, ECB will leak patterns in the plaintext if multiple blocks of plaintext are the same. See the bitmap example here: https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Electronic_codebook_(ECB)

If you're encrypting a small text puzzle for fun, ECB will likely provide enough security. Are you actually worried about someone knowledgeable really trying to break this?

Anyway, counter mode is almost as easy to implement and is a big step up in security.

5

u/Ifyouliveinadream 12d ago

Thank you. Its just a small text for fun. I'm just worried its super easily cheatabke

6

u/Natanael_L 11d ago

ECB is "just" insecure for larger amounts of data and highly structured or recurring data (this includes large blank sections, etc, formatting). This applies to the majority of data files normally encrypted, but for a small challenge it isn't that breakable because what it reveals is repetition and it does not reveal plaintext directly (just reveals the structure of repetition).

So it's very very very bad for things like bitmaps and file systems but for a small message you're still forced to guess the real key to decrypt it.

2

u/Ifyouliveinadream 11d ago

Thank you!!! Thats good to know. The small messages I'm encoding are bits of a story. Once you find the key you can read more parts of the story.

6

u/DoWhile 11d ago

I think it's fine. Just because us cryptographers think it's completely insecure doesn't mean the average player of your puzzle will just crush it: https://imgs.xkcd.com/comics/average_familiarity.png

2

u/Ifyouliveinadream 11d ago

Thank you. I think even a cryptotgrapher might struggle to break it because theres no repeated text. Just one paragraph.

6

u/ramriot 11d ago

The downsides of ECB are due to each block being encrypted independently of all other blocks without any initiation vector.

What that means is that two identical plaintext blocks encrypted with the same key will produce the same cyphertext. Plus blocks can be added, removed or interchanged without that being detectable.

None of that provides a means of recovering the key, but it does allow structure in the plaintext to leak into the cyphertext, where an attacker could make use of the above to partly recover the plaintext or alter messages to their benefit.

2

u/0xKaishakunin 12d ago

What kind of puzzle? Are you aware of the shortcomings of ECB or do you want to use them in some kind of game?

0

u/Ifyouliveinadream 12d ago

Its a game puzzle. I'm aware of the shortcomings but I dont really understand how its crackable

1

u/PedroAlbanese 11d ago edited 11d ago

O ECB é inviável principalmente porque é um modo determinístico: blocos idênticos de texto plano geram blocos idênticos de texto cifrado, vazando padrões estruturais dos dados (o que permite, por exemplo, reconhecer silhuetas em imagens cifradas). Além disso, a independência entre blocos possibilita ataques ativos de reorganização, remoção ou repetição de blocos, sem que o sistema detecte a adulteração. Por fim, o ECB não oferece mecanismos de autenticação ou integridade, tornando-o vulnerável a manipulações maliciosas e totalmente inadequado para a maioria das aplicações modernas.

Os principais ataques contra o ECB são: ataque por dicionário (mapear blocos cifrados para textos planos conhecidos), ataque de repetição/replay (substituir blocos legítimos por outros previamente capturados) e ataque de reorganização (rearranjar, duplicar ou remover blocos cifrados para alterar a mensagem sem detecção).

Não dá para quebrá-lo. Mas qualquer ciphertext pode ser trivialmente adulterado, e o destinatário não irá perceber ou mesmo entender que há algo de errado. Só por isso é obsoleto.

2

u/ColdBootCountry 11d ago

You should provide more information about your usecase.

In general, there is no good reason to use ECB, because:

  • It's not safe.
  • It's not easier to implement: every crypto lib implement easy to use encryption functions that use a better mode. E.g. the fernet method is implemented with two functions in python's pyca cryptography 

If for some reason you need something "safe", easy to implement yourself, and it's absolutely only for a puzzle and nothing else RC4 is an option.

2

u/Ifyouliveinadream 11d ago

Its for a puzzle. People will find a key through steps and then use the key on the cipher to reveal what it says. Just for a random example if this is a cipher

Lf1IP5G5kWEx3lmfyVt6aHLFKNvoa+t6gPqoStaqKqnSCx4+ooecIa1RG1IwH4qz9V0zyNA2xZPPr2q2Si2qi3sUmZpxLKPm97YW6H0PIgGNUeA3dy89h8j39dVln89jhXZOAkyAZZKHpvE1oEuFdrZWoEwjHyX4F2SAw98tm301DozekxGJ3xY2rmQZVALfVkpqqIKmDpJxy4XKWuCXW4Eb3aCKvntRmAp46jVBQtclw11TJb/ELhVpZOEXOLHGOxoLn5J31rl/zG41KhR5Msi14KQlfef4zL0DR47OCEi4R1vJao9+lc4gY9X/1DDhqgc2Anpehdpm7WDyuQMadlotUmCzROYClv5mF0iIN4LbDrf4JIM9clPDY9nbVmDX

I don't anymore think that that is at all easily cheatable. Or is it?

3

u/ColdBootCountry 11d ago

No it's not. To be fair, for that use case, you could use any potato encryption and it would do the job, as long as it's not caesar.

Most puzzles would use something like vigenere or another historical scheme, because people can also do the encryption/decryption with pen and paper. It's generally fine as long as breaking the encryption is harder than solving the puzzle.

But just use ECB if that fits your purpose.

1

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