Generate 256 Bit Key From Passphrase

This post briefly describes how to utilise AES to encrypt and decrypt files with OpenSSL.

  1. Approsto Passphrase Generator
  2. Generate 256 Bit Key From Passphrase Mac

AES - Advanced Encryption Standard (also known as Rijndael).

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  • An ASCII passphrase and SSID are used to generate a 256-bit PSK. OPTIONS ssid The SSID whose passphrase should be derived. Passphrase The passphrase to use. If not included on the command line, passphrase will be read from standard input.
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  • Generating AES 256 bit key value. Does anyone know of a way to get a 256 bit key value generated from a pass phrase of any length? The encryption cannot be salted as the encrypted values need to be generated again and compared in the database. So a value must generate the same encrypted string each time it is encrypted.

OpenSSL - Cryptography and SSL/TLS Toolkit

Subkey generation for 256 bit key

We’ll walk through the following steps:

  • 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).

Approsto Passphrase Generator

The basic command to use is openssl enc plus some options:

  • -P — Print out the salt, key and IV used, then exit
  • -k <secret> or -pass pass:<secret> — to specify the password to use
  • -aes-256-cbc — the cipher name

Note: We decided to use no salt to keep the example simple.

Issue openssl enc --help for more details and options (e.g. other ciphernames, how to specify a salt, …).

Encoding

Let's start with encoding Hello, AES! contained in the text file message.txt:

Decoding

Decoding is almost the same command line - just an additional -d for decrypting:

Note: Beware of the line breaks

While working with AES encryption I encountered the situation where the encoder sometimes produces base 64 encoded data with or without line breaks...

Generate 256 Bit Key From Passphrase Mac

Short answer: Yes, use the OpenSSL -A option.