This might be a noob question, but I couldn't find its answer anywhere online: why does an OpenSSL generated 256-bit AES key have 64 characters? The command I'm using to generate the key is: $ ope. Jul 09, 2014 Demo of AES encryption in both ECB and CBC mode using OpenSSL toolkit. Skip navigation. Secret Key Cryptography - AES using OpenSSL IITB Cyber Security Workshop 2014. (OpenSSL, AES 128, ECB. Generate an AES key plus Initialization vector (iv) with openssl and how to encode/decode a file with the generated key/iv pair Note: AES is a symmetric-key algorithm which means it uses the same key during encryption/decryption. Generate an AES key plus Initialization vector (iv) with openssl and; how to encode/decode a file with the generated key/iv pair; Note: AES is a symmetric-key algorithm which means it uses the same key during encryption/decryption. Generating key/iv pair. We want to generate a 256-bit key and use Cipher Block Chaining (CBC).
I'd like to use the OpenSSL library to decrypt some AES data. The code has access to the key. This project already uses libopenssl for something else, so I'd like to stick to this library.
I went looking directly into /usr/include/openssl/aes.h since the OpenSSL site is light on documentation. The only decrypt function is this one:
Unfortunately, this doesn't have a way to specify the length of the in pointer, so I'm not sure how that would work.
There are several other functions which I believe take a numeric parm to differentiate between encryption and decryption. For example:
From what I understand using Google, the enc parm gets set to AES_ENCRYPT or AES_DECRYPT to specify which action needs to take place.
Which brings me to my 2 questions:
unsigned char *ivec parm needed for most of these, and where do I get it from?There's no size given because the block sizes for AES are fixed based on the key sizedownload skype for android tablet 4.0 3 ; you've found the ECB mode implementation, which isn't suitable for direct use (except as a teaching tool).
ECB, CBC, CFB128, etc, are all short names for the modes of operation that are in common use. They have different properties, but if you never touch ECB mode, you should be alright.
I suggest staying further away from the low-level code; use the EVP_* interfaces instead, if you can, and you can move some of these decisions into a text configuration file, so your users could easily select between the different ciphers, block sizes, and modes of operation if there should ever be a good reason to change away from the defaults.
My sympathies, OpenSSL documentation feels worse than it is, and it isn't that great. You may find Network Security with OpenSSL a useful book. I wish I had found it sooner the last time I needed to use OpenSSL. (Don't let the silly title fool you -- it should have been titled just 'OpenSSL'. Oh well.)
Edit I forgot to mention the initialization vectors. They are used to make sure that if you encrypt the same data using the same key, the ciphertext won't be identical. You need the IV to decrypt the data, but you don't need to keep the IV secret. You should either generate one randomly for each session (and send it along with an RSA or El Gamal or DH-encrypted session key) or generate it identically on both endpoints, or store it locally with the file, something like that.
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| Demonstrates how to use RSA to protect a key for AES encryption. It can be used in this scenario: You will provide your RSA public key to any number of counterparts. Your counterpart will generate an AES key, encrypt data (or a file) using it, then encrypt the AES key using your RSA public key. Your counterpart sends you both the encrypted data and the encrypted key. Since you are the only one with access to the RSA private key, only you can decrypt the AES key. You decrypt the key, then decrypt the data using the AES key. This example will show the entire process. (1) Generate an RSA key and save both private and public parts to PEM files. (2) Encrypt a file using a randomly generated AES encryption key. (3) RSA encrypt the AES key. (4) RSA decrypt the AES key. (5) Use it to AES decrypt the file or data.
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