How do I make openssl_encrypt pad the input to the required block size?

Question

My code works if I manually pad my string to the length of 32.
My question is: Is there a way to make the openSSL pad the data, or do I always have to do it for it?

Answer 1

As Luke Park said, instead of explicitly telling openssl_encrypt to use OPENSSL_ZERO_PADDING, simply remove that option from the parameter and it will default to the PKCS #7 padding scheme (fills the rest of the block with 0x0n where n is the number of bytes necessary; + 16 0x00 if the block is already complete). Note: PKCS #5 as referenced by Luke and PKCS #7 are effectively identical in this scenario.

From PHP docs:

Without using OPENSSL_ZERO_PADDING, you will automatically get PKCS#7 padding.

So you should be calling:

openssl_encrypt("my baba is over the ocean", 'AES-256-CBC', $MY_SECRET_KEY, OPENSSL_RAW_DATA, $MY_IV);