Add the ability for the CLI to "guess" the version of the codec used …

…to encode the file.

Note that, when it reads a value larger than the current maximum version, it will assume it is a v1 file for legacy reasons.

Edited the codecs to no longer validate the version when decoding. This will allow people to tamper with the header (for whateve reason) and still successfully decode the file.

psistega3-cli/src/error.rs

@@ -16,6 +16,10 @@ pub enum Error {
     InvalidVersion,
     /// The supplied passwords did not match.
     PasswordMismatch,
+    /// Version guessing is not supported for encoding files.
+    NoVersionGuessing,
+    /// Version guessing failed to find a valid version.
+    VersionGuessingFailed,
 }
 
 impl fmt::Display for Error {
@@ -30,6 +34,8 @@ impl fmt::Display for Error {
             Error::PasswordMismatch => {
                 "The entered passwords did not match. Please check and try again."
             }
+            Error::NoVersionGuessing => "Version guessing is not supported for encoding files.",
+            Error::VersionGuessingFailed => "Version guessing failed to find a valid version.",
         })
     }
 }

psistega3-cli/src/main.rs

@@ -3,16 +3,23 @@ mod error;
 
 use crate::error::{Error, Result};
 
-use psistega3_core::codecs::codec::{Codec, Config};
-use psistega3_core::codecs::v1::StegaV1;
-use psistega3_core::codecs::v2::StegaV2;
-use psistega3_core::version::*;
+use psistega3_core::{
+    codecs::{
+        codec::{Codec, Config},
+        v1::StegaV1,
+        v2::StegaV2,
+    },
+    utilities::png_utils::{self, PngChunkType},
+    version::*,
+};
 
 use simple_logger::SimpleLogger;
 use std::{convert::TryFrom, env, io::stdin};
 
 /// The prompt for confirming a yes/no option.
 const CONFIRM_PROMPT: &str = "Are you sure you wish to enable this feature?";
+/// The current highest codec version.
+const CURRENT_MAX_VERSION: u8 = 0x2;
 
 //ooneporlygs
 
@@ -86,7 +93,21 @@ fn main() {
     if needs_codec {
         let mut codec_version: Option<Version> = None;
         if &args[2] == "-v" {
-            let version = &args[3];
+            let mut version = args[3].clone();
+
+            // Have we been asked to guess the version, based on the file itself?
+            if version.to_uppercase() == "GUESS" {
+                if action_type == ActionType::Encode {
+                    show_abort_message(Error::NoVersionGuessing);
+                }
+
+                if let Some(v) = read_bkgd_chunk(&args[5]) {
+                    version = v;
+                } else {
+                    show_abort_message(Error::VersionGuessingFailed);
+                }
+            }
+
             if let Ok(v) = version.parse::<u8>() {
                 if let Ok(cv) = Version::try_from(v) {
                     codec_version = Some(cv);
@@ -136,6 +157,26 @@ fn main() {
     }
 }
 
+fn read_bkgd_chunk(path: &str) -> Option<String> {
+    let chunk = png_utils::read_chunk_raw(path, PngChunkType::Bkgd)?;
+
+    // We have a bKGD chunk to process!
+    let data = png_utils::get_chunk_data(&chunk)?;
+
+    if data.len() < 6 {
+        return None;
+    }
+
+    // This could be a legacy file, so we can assume that it is a V1 file here.
+    // In a v1 file the specific segment could be anything, as it was randomly generated.
+    if data[5] > CURRENT_MAX_VERSION {
+        return Some("1".to_string());
+    }
+
+    // Since the versions are zero-indexed, we need to add one here to get the correct version.
+    Some((data[5] + 1).to_string())
+}
+
 /// Apply any specified codec settings.
 ///
 /// # Arguments
@@ -506,6 +547,12 @@ fn show_examples() {
     println!("You will be prompted for a password after executing this command.");
     println!("If any data was successfully decoded then it will be displayed on screen.");
     println!("{split}");
+    println!("psistega3 -d -v GUESS \"C:\\reference.png\" \"C:\\encoded.png\"");
+    println!();
+    println!("This command will attempt to guess the version, based on the file contents. If this fails, it will default to v1 file for legacy reasons.");
+    println!("You will be prompted for a password after executing this command.");
+    println!("If any data was successfully decoded then it will be displayed on screen.");
+    println!("{split}");
     println!(
         "psistega3 -ef -v 1 \"C:\\reference.png\" \"C:\\encoded.png\" \"C:\\input_file_path.foo\""
     );

psistega3-core/src/codecs/v1.rs

@@ -580,7 +580,7 @@ impl StegaV1 {
     ///
     /// * `path` - The path to the PNG file.
     ///
-    pub fn process_bkgd_chunk(&mut self, path: &str) -> bool {
+    pub(crate) fn process_bkgd_chunk(&mut self, path: &str) -> bool {
         let Some(chunk) = png_utils::read_chunk_raw(path, PngChunkType::Bkgd) else {
             // This is an error as we should always have a bKGD chunk.
             return false;
@@ -597,9 +597,6 @@ impl StegaV1 {
             return false;
         }
 
-        // NOTE: in v2 and beyond we will enforce the version here, but for this legacy
-        // version we will not do so.
-
         // The 1st bit are be stored in byte 1.
         // Bit 1 stores the flag indicating whether the file locker should be
         //   used with this file.

psistega3-core/src/codecs/v2.rs

@@ -580,7 +580,7 @@ impl StegaV2 {
     ///
     /// * `path` - The path to the PNG file.
     ///
-    pub fn process_bkgd_chunk(&mut self, path: &str) -> bool {
+    pub(crate) fn process_bkgd_chunk(&mut self, path: &str) -> bool {
         let Some(chunk) = png_utils::read_chunk_raw(path, PngChunkType::Bkgd) else {
             // This is an error as we should always have a bKGD chunk.
             return false;
@@ -597,11 +597,6 @@ impl StegaV2 {
             return false;
         }
 
-        if data[5] != CODED_VERSION {
-            // The codec version does not match.
-            return false;
-        }
-
         // The 1st bit are be stored in byte 1.
         // Bit 1 stores the flag indicating whether the file locker should be
         //   used with this file.

psistega3-core/src/utilities/png_utils.rs

@@ -6,7 +6,7 @@ use std::fs::File;
 use super::{file_utils, misc_utils};
 
 #[allow(dead_code)]
-pub(crate) enum PngChunkType {
+pub enum PngChunkType {
     Bkgd,
     Idat,
 }
@@ -96,7 +96,7 @@ pub(crate) fn generate_bkgd_chunk(data: &[u8]) -> Vec<u8> {
 ///
 /// * `data` - The contents of the PNG chunk.
 ///
-pub(crate) fn get_chunk_data(data: &[u8]) -> Option<&[u8]> {
+pub fn get_chunk_data(data: &[u8]) -> Option<&[u8]> {
     let data_len = get_chunk_length(data)?;
 
     let start = 8;
@@ -168,7 +168,7 @@ pub fn insert_or_replace_bkgd_chunk(path: &str, data: &[u8]) -> Result<()> {
 ///
 /// `Note:` this function is only designed to read the **first** instance of the chunk present within the file.
 ///
-pub(crate) fn read_chunk_raw(path: &str, chunk_type: PngChunkType) -> Option<Vec<u8>> {
+pub fn read_chunk_raw(path: &str, chunk_type: PngChunkType) -> Option<Vec<u8>> {
     // If we have a chunk present then the index of
     // the header will be returned.
     let start = find_chunk_start(path, chunk_type)?;