I have a log of a programs state. This log can be manualy or time interval saved on a file for persistant storage. Before saving it to the file it is encrypted with RNCryptor.
My current appending(saving) to file flow:
What I imagine:
When I read this I will have to build a string from all the encoded strings. But I don't know how to decrypt the file with multiple encrypted blocks in it. How to differentiate where one ends and another begins. Also is this the best performance choice. The text in the file at maximum could get to 100MB(Possibly it will never get this big). Is using Core Data viable? Each append as different record or something. And core data could be encrypted so no need for RNCryptor.
Would appreciate code in Objective-C if any.
There are many things you can do:
Easiest would be to encode the ciphertexts to text (e.g. with Base64) and write each encoded ciphertext to a new line. You need encoding for that, because the ciphertext itself might contain bytes that can be interpreted as newline control characters, but that won't happen with a text encoding. The problem with this is that it blows up the logs unnecessarily (e.g. by 33% if Base64 is used)
You can prepend each unencoded ciphertext with its length (e.g. big-endian int32 encoding) and write both as-is to a file in binary mode. If you begin reading the file from the beginning, then you can distinguish each ciphertext, because you know how long the following ciphertext is and when the next encoded length starts. The blowup is only as big as the encoding of the ciphertext length for each ciphertext.
Use a binary delimiter such as 0x0101 between ciphertexts, but such a delimiter might still appear in the ciphertexts, so you need to escape it if you find it somewhere in the ciphertext. This is a little tricky to get right.
If the amount of logs is small (few MB), then you can find a library to append to a ZIP file.