Timeline for How to decrypt a file when I have its key?
Current License: CC BY-SA 3.0
9 events
| when toggle format | what | by | license | comment | |
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| Jul 23, 2014 at 7:00 | comment | added | dave_thompson_085 | When you logically reverse the (correct) figure you posted, you can see that the IV only affects decryption of the first block; decryption of all other blocks depends only on the key and the preceding ciphertext, which OP has. In the 1960's when modes like CBC and OFB were created, most crypto was done at a low level subject to bit errors, and "error [non]propagation" was an important feature; see en.wikipedia.org/wiki/… for a DIFFERENT mode that WOULD be unrecoverable without IV. | |
| Jul 19, 2014 at 6:58 | comment | added | user45139 | @dave_thompson_085 You need either the valid password used to create the key, or a combination of the key with the correct IV (which thing is rather generated by encryption software, most of the time, so it is too difficult if not impossible to get it) | |
| Jul 19, 2014 at 5:06 | comment | added | dave_thompson_085 | If you decrypt CBC with the wrong IV (e.g. all zeros) the first block (16 bytes for AES) is garbage but the rest is correct. Most (types of) computer files have low entropy in the first 4 bytes and often a few more, so guessing the first block isn't totally crazy. (The same would be true for CFB, which is rarely used, but not CTR, or CTR-based modes like GCM and CCM, or OFB.) | |
| Jul 18, 2014 at 13:31 | history | edited | user45139 | CC BY-SA 3.0 |
added 13 characters in body
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| Jul 18, 2014 at 9:45 | history | edited | user45139 | CC BY-SA 3.0 |
added 30 characters in body
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| S Jul 17, 2014 at 12:37 | history | suggested | mdeous | CC BY-SA 3.0 |
embed image in post instead of linking
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| Jul 17, 2014 at 12:32 | review | Suggested edits | |||
| S Jul 17, 2014 at 12:37 | |||||
| Jul 17, 2014 at 10:04 | vote | accept | CommunityBot | ||
| Jul 17, 2014 at 10:00 | history | answered | user45139 | CC BY-SA 3.0 |