how to use OpenSSL to decrypt Java AES-encrypted data?

Question

I\'m interfacing to a legacy Java application (the app cannot be changed) which is encrypting data using AES. Here is how the original Java code is instantiating the AES ci

Answer 1

Possible answer found:

"By default, Java Ciphers (at least in Sun's implementations) are constructed in what is called Electronic Codebook (ECB) mode." (Source: http://www.javamex.com/tutorials/cryptography/block_modes.shtml)

So if ECB is used by default, I guess that means no initialization vector, and I can use the following method from OpenSSL:

void AES_ecb_encrypt(*in, *out, *key, enc);

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Using AES_decrypt() I can decrypt 1000+ byte messages that originated on the Java side. So it looks like Java does indeed default to ECB mode with no initialization vector. However, I still cannot encrypt and send a new message to the Java app. Investigation continues.

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Got it all working. Thanks for the numerous hints. I can confirm Java uses ECB by default. All padding bytes are set to the number of bytes added (which is known as PKCS5-padding). "Hello World" -> encrypted by Java -> decrypted using OpenSSL will look like "Hello World\5\5\5\5\5".