RISC-V Encryption

XOR-based cipher in a single RISC-V assembly file (xor_cipher.s). Encrypts plaintext with a 4-byte repeating key (e.g. "SU00"), decrypts into a buffer, then compares and prints plain, cipher, and deciphered strings via ecall. Key derivation: per-byte nibble swap and masking; encryption/decryption is XOR with that key. For RARS or Venus. Demonstrates low-level assembly: data layout, loops, branching, and system calls on RISC-V.

Data and main The .data section holds plaintext, password, cipher and deciphered buffers (.space 128), and string labels for output. main loads base addresses into s0–s3, calls ENCRYPT (plain, password, cipher, key index), then DECRYPT (password, cipher, deciphered), then COMPARE (plain, deciphered).

ENCRYPT Loop: load a byte from plain; if null, return. Key index cycles 0–3; each byte uses one password byte. The key byte is transformed (nibble swap, mask 0xEE); the plain byte is XORed with it and stored to cipher. DECRYPT uses the same key derivation and XORs cipher bytes into the deciphered buffer.

COMPARE Byte-by-byte comparison of plain and deciphered. On match to end-of-string, print all three strings (plain label, plaintext, cipher label, ciphertext, deciphered label, deciphered text) via ecall 4 and return; on mismatch, set result and return.