RNCryptor PHP encrypt function returns invalid base64 data

Question

I'm using RNCryptor for cryptography in an iOS project. The app decrypts JSON strings sent from a server. On the server, the strings are encrypted using unmodified versions of the PHP functions found in the RNCryptor repo.

Using the same password for encrypting all strings, the returned base64 data is sometimes invalid for different JSON strings I pass in to the RNCryptor PHP encrypt function. On the app, I see this error when trying to decrypt the data from the server: "The operation couldn’t be completed. (net.robnapier.RNCryptManager error -4301.)"

To show you some examples, this base64 string gets successfully decrypted:

AwHwsZqlDpvAcmWX92UtkQSKcHOq18gLsLFtP4FujV3DtXVrtGL86CFY9KAs23HaAoYINTLH3ouUJPpyQEcfXni+rJUJghTFBB24kk52aU0GQ/8IIgfnXPUywUuNwD4n7DnweaS3DdmdhFBQIUpSaCEg4T5bMPhIvUAndVMvJwc/SjbhJoB+bUqRDcPYXPzMiEW1i4jea/ssE87PcX9/NZtfkoNyiY7KLRy/dhgsADde1Q==

This one, however, fails:

AwHH7y0mnQvtWNCKa73jnS2DG63ylqDBc5iema3G6+/EkwPxiIkrPQHyJLvd3MO3mMIPsJjDK1C3uBCoHDc+Gzm0NJhBa08zs1twzZQ1jBdyt/q2AnGX99nku7MqF1oJOJ8nN1lriwYcFyvjBoBkEAAG28umjwxb5Y1t29dXtJzCwsrEVERs+SNkRE5C/j++bMPTV28EmR7LviyaMFAzpT+F5yUlLp2zRQgaQfyG8RlJTcvc+IqsrOisrDn7umDg+ii/Z9GDLlMkhu7OL1lHfcmD

It seems only the base64 strings that have the "=" character get decrypted successfully. Again, I used the same password to encrypt & decrypt these two strings. Why is the PHP encrypt function behaving like this?

P.S. The JSON strings passed in are perfectly valid (generated using the PHP json_encode() function).

Answer 1

After much debugging, the issue turned out to be the base64 decoder I was using on iOS. I was initially using the NSData+Base64 category from this blog post. It's flawed.

I ended up using the implementation here. Everything decrypts just fine now. :)