One cross-platform encryption method would be to use OpenSSL (https://www.openssl.org/). The Linux user might use the following commands. Encryption: openssl aes-256-cbc -pbkdf2 -iter 1000000 -in plaintext.txt -out ciphertext.txt Decryption: openssl aes-256-cbc -pbkdf2 -iter 1000000 -d -in ciphertext.txt -out plaintext.txt I think the two commands will be the same on a Windows machine. Assuming both sides have agreed on a decent password, this should be very secure. The main difficulty for a non-technical Windows user would probably be installing OpenSSL; the easiest way might be via a trusted third-party binary distribution. I'm assuming the OP is content with a symmetric cipher (he or she didn't say). Best regards, Greg Marks
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