The Salt is written as part of the output, and we will read it back in the next section. This is because a different (random) salt is used. ![]() This will result in a different output each time it is run. $ openssl enc -aes-256-cbc -in plaintext.txt -base64 -md sha1 We will use the password 12345 in this example. SHA1 will be used as the key-derivation function. The output will be written to standard out (the console). The following command will prompt you for a password, encrypt a file called plaintext.txt and Base64 encode the output. To encrypt a plaintext using AES with OpenSSL, the enc command is used. Command line OpenSSL uses a rather simplistic method for computing the cryptographic key from a password, which we will need to mimic using the C++ API. OpenSSL uses a hash of the password and a random 64bit salt. Key stretching uses a key-derivation function. ![]() Because humans cannot easily remember long random strings, key stretching is performed to create a long, fixed-length key from a short, variable length password. The cryptographic keys used for AES are usually fixed-length (for example, 128 or 256bit keys). ![]() In this tutorial we will demonstrate how to encrypt plaintext using the OpenSSL command line and decrypt the cipher using the OpenSSL C++ API. Symmetric-key algorithms are algorithms for cryptography that use the same cryptographic keys for both encryption of plaintext and decryption of ciphertext. AES ( Advanced Encryption Standard) is a symmetric-key encryption algorithm.
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