Using `openssl rand` and `openssl rand -base64` both generate cryptographically secure pseudo-random bytes, but they differ in how the output is encoded and formatted.
OpenSSL Rand**
- Purpose: Generates pseudo-random bytes directly. This command uses a cryptographically secure pseudo-random number generator (CSPRNG) seeded by the operating system's entropy sources[2][5].
- Output: The output is raw binary data. This can be useful for applications requiring raw random bytes, such as generating keys or salts.
- Usage: You can specify the number of bytes to generate, and the output will be in binary format unless otherwise specified.
OpenSSL Rand with Base64 Encoding**
- Purpose: Generates pseudo-random bytes and encodes them in Base64 format. This is useful for representing binary data as text, which can be easier to handle in certain contexts, such as in configuration files or when sending data over text-based protocols.
- Output: The output is encoded in Base64, which means it uses a character set that includes letters (both uppercase and lowercase), numbers, and a few special characters (+ and /). This encoding increases the size of the output compared to raw binary, as it requires more characters to represent the same amount of data.
- Usage: Similar to the basic `rand` command, but with the `-base64` option. For example, `openssl rand -base64 20` generates 20 bytes of random data and encodes them in Base64.
Key Differences
- Encoding: The primary difference is the encoding of the output. `openssl rand` produces raw binary data, while `openssl rand -base64` encodes this data in Base64.
- Use Cases: Raw binary output is suitable for applications requiring direct binary data, such as cryptographic key generation. Base64 encoding is useful when the output needs to be represented as text, such as in web applications or when sending data over text-based protocols.
- Size: Base64 encoding increases the size of the output compared to raw binary. For example, encoding 20 bytes of binary data in Base64 will result in a string of approximately 28 characters (since Base64 encoding uses 4 characters to represent every 3 bytes of data).
In summary, both commands generate secure random bytes, but the choice between them depends on whether you need raw binary data or a text representation of that data.
Citations:
[1] https://crypto.stackexchange.com/questions/68919/is-openssl-rand-command-cryptographically-secure
[2] https://www.openssl.org/docs/man1.1.1/man1/rand.html
[3] https://docs.openssl.org/1.1.1/man7/RAND_DRBG/
[4] https://docs.openssl.org/3.1/man7/RAND/
[5] https://www.misterpki.com/openssl-rand/
[6] https://crypto.stackexchange.com/questions/105796/fast-and-secure-pseudo-random-generator-with-linux-tools
[7] https://doc.ecoscentric.com/ref/openssl-crypto-rand.html
[8] https://unix.stackexchange.com/questions/518617/how-to-use-openssl-random-key-in-bash-script