# Decrypt AES-128 with key file but missing IV? [duplicate]

I want to decrypt a file that has been encrypted using AES-128 in CBC mode using OpenSSL. I got the “.key” file – which is 32 digits – but when I try to decrypt with OpenSSL, the program asks me for “-iv” and I don't know the IV of that file so it won't decrypt. Is there is any other way to decrypt the file without knowing the IV?

I tried with another file of which I have the correspondent IV and it works, and when I don't supply that IV, the decryption fails too.

By the way: is there anyway to know what type of encryption was used to encrypt a file?

• Sorry is IV NO VI :P – BelindaSchull Apr 1 '14 at 16:42
• Try ECB mode, and then try the all-zero IV. $\;$ – user991 Apr 1 '14 at 17:26
• @RickyDemer And how's that going to help her decrypt the file that's already encrypted using CBC with a IV she doesn't know/have? – e-sushi Apr 1 '14 at 17:27
• Oh, I didn't notice the CBC mode part. $\:$ The all-zero IV would be a workable "default", such as if the key was only used once. $\;\;\;\;$ – user991 Apr 1 '14 at 17:30

• @BelindaSchull if you start with encfile, say, to get the IV do (one of many possible commands) iv=$(od -tx1 -An -N 16 encfile | tr -d ' ') and make a new cipher file encfile2 by dd if=encfile of=encfile2 bs=1 skip=16 and to decrypt openssl enc -d -aes-128-cbc -K ..... -iv${iv} -in encfile2 -out encfile2.out filling in your key on the dots (as hexstring), so if k.key is a 16 byte key file, use $k after setting it by k=$(od -tx1 -An k.key | tr -d ' ') e.g. – Henno Brandsma Jul 20 '19 at 9:05