Timeline for ISO 9564-1 format 4: do I need an IV?
Current License: CC BY-SA 3.0
11 events
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| Feb 13, 2017 at 13:00 | history | edited | Maarten Bodewes♦ | CC BY-SA 3.0 |
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| Feb 13, 2017 at 12:41 | comment | added | Michael | It is very clear, actually. Thank you for the explanation! | |
| Feb 13, 2017 at 12:41 | vote | accept | Michael | ||
| Feb 13, 2017 at 12:39 | comment | added | Maarten Bodewes♦ | I've changed the sentence to prefixing the IV to the ciphertext. This IV is the first value of the nonce + counter in the picture included. Sorry, I don't have any easy tools to paint a picture for this, which would make it easier to understand. | |
| Feb 13, 2017 at 12:36 | history | edited | Maarten Bodewes♦ | CC BY-SA 3.0 |
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| Feb 13, 2017 at 12:36 | comment | added | Michael | Yes, that's why I do not understand the sentence "Prefixing a (16 byte) random IV however does make sense", or did you not mean anything with it specifically? | |
| Feb 13, 2017 at 12:28 | comment | added | Maarten Bodewes♦ | A random value added (concatenated) to the PIN will NOT act as an IV, this is what I'm trying to tell you. The IV in CTR mode is used as initial value for the counter. | |
| Feb 13, 2017 at 12:26 | comment | added | Michael | Partially: why would it make sense to do that in AES-CTR? As you explain in the other paragraphs, this IV will then just be XOR'ed with the key stream. If we assume that the key stream is based on the key and the IV, and that the IV is sent along with the cipher text, what would be the sense of prefixing the IV with the plain text? | |
| Feb 13, 2017 at 12:20 | comment | added | Maarten Bodewes♦ | There is a difference between prefixing any random value and prefixing the IV used for the mode of operation. The former is not what you want but as the IV can be public there is no reason why you could not prefix it (or store it otherwise with the ciphertext). Does this clear it up? | |
| Feb 13, 2017 at 12:18 | comment | added | Michael | Thanks for your answer. I don't fully get your last paragraph: it seems to contradict the other paragraphs. Prefixing/appending an IV might make sense in AES-CBC, but it won't probably make any sense when using AES-CTR. That is clear. However, in the last paragraph you seem to suggest that prefixing a random value does make sense, or do you mean 'adding' instead of 'prefixing'? | |
| Feb 13, 2017 at 11:33 | history | answered | Maarten Bodewes♦ | CC BY-SA 3.0 |