![]() ![]() #Encrypto decrypt key iv codeYou can have a look at the source code here to get an idea how the key and IV derivation takes place ( EVP_BytesToKey is not described that well, it is a proprietary mechanism within OpenSSL). The salt is a piece of random bytes generated when encrypting, stored in the file header upon decryption, the salt is retrieved from the header, and the key and IV are re-computed from the provided password and salt. It makes sure that the key and IV are always different, even if you use the same password. The salt is an input parameter to the PBKDF. ![]() This is a function akin to PBKDF1 which doesn't use many iterations. In the case of OpenSSL the method used is EVP_BytesToKey. The key and IV are both calculated from the password using a PBKDF. Therefore the second question is: how does the decryption program know the iv which is needed to decrypt the file? Or, to put it differently, if the iv is embedded in the encrypted file (like the salt is), how is it done? Now, while I can see the salt in the encrypted file and I provide the key to the program, I do not type the iv nor I can see the iv in the encrypted file. Openssl enc -d -aes128 -in file2.enc -out -pĪnd I get the same WITHOUT providing the iv! salt=237F07334625A768 AES provides 128 bit, 192 bit and 256 bit of secret key size for encryption. If you don't have a handy way to separate the IV and ciphertext in your. The IV needs to be unique (with a given key) and for some cipher modes also needs to be unpredictable, but it does not need to be secret sending it in plain text alongside the ciphertext is fine. Hence, you must always use an IV of 128 bits (16 bytes) with AES. Either prepending or appending the IV is standard practice. ![]() Openssl enc -aes128 -in file.txt -out file2.enc -p When a symmetric cipher mode requires an IV, the length of the IV must be equal to the block size of the cipher. Now I do the same (same plaintext, same key) without providing the iv: Which is its relation with my key "1234"? (It looks an md5 hash. Using IV we randomize the encryption of similar blocks. Openssl enc -d -aes128 -iv BABA -in file1.enc -out -pĪnd obviously I get the same salt, key and iv as before.įirst question is: in which sense "0326A1E8F4875B26FE2D04E02425C5AD" is the "key"? The AES engine requires a plain-text and a secret key for encryption and same secret key is used. Openssl enc -iv BABA -aes128 -in file.txt -out file.enc -p Suppose I encrypt with a key "1234" a file containing "abcd" with: ![]()
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