README
These are encryption / decryption samples for the gcrypt library.
They can be used as a standalone project for
key generation / encryption / decryption.
FILES
keygen -- Key generator.
asencrypt -- Asymmetric encryption with public key.
asdecrypt -- Asymmetric decryption with private key.
Encryption:
asencrypt.exe -i infile.txt -o outfile.enc testkey.pub
Decryption:
asdecrypt.exe -i infile.enc -o outfile.dec -p password_for_key testkey.key
See Makefile for typical usage. The programs will print basic usage information on request.
BUILD
All the files are built on Windows using MSYS and MinGW. The files should build on linux and variants with little modification.
PREP
Build the glibcrypt library first. This project will look for the built libs and includes in the .lib subdir under the original build directories. This allows installation-less build. (for test and experimentation)
NOTABLES
I made a small malloc subsystem. It can be used to detect leaks very easily. Use zalloc() like you would use malloc(). If you make an alloc mistake, this malloc gently prints a string like:
zmalloc: Memory leak on gcry.c at line 711 (0x010A1178)
Also created a base64 encode / decode subsystem. See headers and source for more info.
FILE FORMAT
The output format of the encrypted file is base64 line aligned to 64 char length. The header and trailer line contains the RSA string delimiter. "-----BEGIN GCRYPT RSA CYPHER-----" etc ... Under the hood the file is in chunks, determined by the key size. The chunk starts with a two byte length and data follows. The next chunk start is calculated from the length of the current chunk. Like this:
LEN LEN DATA ..... DATA LEN LEN DATA ....
|------------------------|
This is the simplest (I think) way to adapt tho the variable length output of the asymmetric encryption.
TESTING
'make tests' will build the needed files and execute a diff on generated outputs. It is comparing them with expected output of the original files. Test passes if the diffs are silent.
FEEDBACK
This code was developed for a larger project. However, taming the library is a common task, so I shared it ...