iOS - How to generate random IV in ECB mode?

Question

I want to generate random IV in iOS which is base on the below code:

mcrypt_create_iv(mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_ECB), MCRYPT_RAND);

Is anybody can tell me how to generate random IV in iOS same with the above php? Thank you.

[ECB](https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Electronic_Codebook_.28ECB.29) doesn't use an IV, so you can just use an empty string. — Artjom B., Mar 21 '16 at 08:54
**Never use [ECB mode](http://crypto.stackexchange.com/q/14487/13022)**. It's deterministic and therefore not semantically secure. You should at the very least use a randomized mode like [CBC](http://crypto.stackexchange.com/q/22260/13022) or [CTR](http://crypto.stackexchange.com/a/2378/13022). It is better to authenticate your ciphertexts so that attacks like a [padding oracle attack](http://crypto.stackexchange.com/q/18185/13022) are not possible. This can be done with authenticated modes like GCM or EAX, or with an [encrypt-then-MAC](http://crypto.stackexchange.com/q/202/13022) scheme. — Artjom B., Mar 21 '16 at 08:55

score 0 · Answer 1 · edited May 23 '17 at 11:59

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This question is unanswerable (it's akin to "what is the sound of one hand clapping?"), but in the interest of guiding people who come upon it in the future:

As Artjom B. pointed out in the comments, ECB mode doesn't accept an IV
Don't write crypto code (the entire CryptoFails blog is worth reading)
ECB mode sucks for security

What to do instead: See this answer.

edited May 23 '17 at 11:59

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answered Mar 21 '16 at 15:10

Scott Arciszewski

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Understood. Thank you. – JacksonNg Mar 22 '16 at 01:13

iOS - How to generate random IV in ECB mode?

1 Answers1