With the help of OpenSSL you can easily encrypt and decrypt files. This method of encryption is of course also compatible with the openssl binaries you can download for the Windows platform. Use base64 encoding for better multi-plaform exchange.
Encrypt files with (a password is asked for encrypting):
openssl enc -aes-256-cbc -base64 -in <file to encrypt> -out <encrypted file>
Decrypt files with (a password is asked for decrypting):
openssl enc -aes-256-cbc -base64 -d -in <encrypted file> -out <decrypted file>
The commands above use base64 encoding for storing the encrypted data.