Minimal verifiable compression using lz4_flex

Cargo.toml

@@ -15,6 +15,8 @@ common = { path = "common" }
 chacha20 = "0.9.1"
 hex-literal = "1.0.0"
 
+lz4_flex = "0.11"
+
 risc0-zkvm = { version = "2.0",  default-features = false, features = ['std'] }
 risc0-build = "2.0"
 tracing-subscriber = { version = "0.3", features = ["env-filter"] }

host/Cargo.toml

@@ -12,6 +12,7 @@ hex-literal.workspace = true
 risc0-zkvm = { workspace = true,  default-features = true }
 tracing-subscriber.workspace = true
 serde.workspace = true
+lz4_flex.workspace = true 
 
 [features]
 cuda = ["risc0-zkvm/cuda"]

host/src/main.rs

@@ -1,6 +1,7 @@
 use chacha20::cipher::{KeyIvInit, StreamCipher};
 use chacha20::ChaCha20;
 
+use lz4_flex::decompress_size_prepended;
 // These constants represent the RISC-V ELF and the image ID generated by risc0-build.
 // The ELF is used for proving and the ID is used for verification.
 use methods::GUEST_ENCRYPT_ELF;
@@ -74,7 +75,10 @@ fn main() {
     // decrypt ciphertext by applying keystream again
     cipher.apply_keystream(&mut output_buffer);
 
-    assert_eq!(output_buffer, plaintext);
+    let decompressed_output =
+        decompress_size_prepended(&output_buffer).expect("Unable to decompress output");
+
+    assert_eq!(decompressed_output, plaintext);
     println!("Decryption of zkVM ciphertext matches input!");
     println!(
         "Output size to publish to DA = {} bytes (seal), {} bytes (ciphertext)",

methods/guest/Cargo.toml

@@ -6,5 +6,7 @@ edition.workspace = true
 [dependencies]
 common.workspace = true
 
+lz4_flex.workspace = true 
+
 risc0-zkvm = { workspace = true,  default-features = false, features = ['std'] }
 chacha20.workspace = true

methods/guest/src/main.rs

@@ -1,5 +1,6 @@
 use chacha20::cipher::{KeyIvInit, StreamCipher};
 use chacha20::ChaCha20;
+use lz4_flex::compress_prepend_size;
 use risc0_zkvm::{
     guest::env,
     sha::{Impl, Sha256},
@@ -25,15 +26,16 @@ fn main() {
     // TODO:
     // - Hash key and/or nonce & commit?
 
+    let mut compressed_input = compress_prepend_size(&buffer);
     // Key and IV must be references to the `GenericArray` type.
     // Here we use the `Into` trait to convert arrays into it.
     let mut cipher = ChaCha20::new(&key.into(), &nonce.into());
 
     // Write ciphertext into buffer by applying keystream to plaintext
-    cipher.apply_keystream(&mut buffer);
+    cipher.apply_keystream(&mut compressed_input);
 
     // write public output to the journal
-    env::commit_slice(&buffer);
+    env::commit_slice(&compressed_input);
 
     let end = env::cycle_count();
     eprintln!("*-*-*-* CYCLE COUNT: {}", end - start);