Add comprehensive security tests for masking and shape hardening features

- Introduced red-team expected-fail tests for client masking shape hardening.
- Added integration tests for masking AB envelope blur to improve obfuscation.
- Implemented masking security tests to validate the behavior of masking under various conditions.
- Created tests for masking shape above-cap blur to ensure proper functionality.
- Developed adversarial tests for masking shape hardening to evaluate robustness against attacks.
- Added timing normalization security tests to assess the effectiveness of timing obfuscation.
- Implemented red-team expected-fail tests for timing side-channel vulnerabilities.

src/config/tests/load_mask_shape_security_tests.rs

@@ -0,0 +1,195 @@
+use super::*;
+use std::fs;
+use std::path::PathBuf;
+use std::time::{SystemTime, UNIX_EPOCH};
+
+fn write_temp_config(contents: &str) -> PathBuf {
+    let nonce = SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .expect("system time must be after unix epoch")
+        .as_nanos();
+    let path = std::env::temp_dir().join(format!("telemt-load-mask-shape-security-{nonce}.toml"));
+    fs::write(&path, contents).expect("temp config write must succeed");
+    path
+}
+
+fn remove_temp_config(path: &PathBuf) {
+    let _ = fs::remove_file(path);
+}
+
+#[test]
+fn load_rejects_zero_mask_shape_bucket_floor_bytes() {
+    let path = write_temp_config(
+        r#"
+[censorship]
+mask_shape_bucket_floor_bytes = 0
+mask_shape_bucket_cap_bytes = 4096
+"#,
+    );
+
+    let err =
+        ProxyConfig::load(&path).expect_err("zero mask_shape_bucket_floor_bytes must be rejected");
+    let msg = err.to_string();
+    assert!(
+        msg.contains("censorship.mask_shape_bucket_floor_bytes must be > 0"),
+        "error must explain floor>0 invariant, got: {msg}"
+    );
+
+    remove_temp_config(&path);
+}
+
+#[test]
+fn load_rejects_mask_shape_bucket_cap_less_than_floor() {
+    let path = write_temp_config(
+        r#"
+[censorship]
+mask_shape_bucket_floor_bytes = 1024
+mask_shape_bucket_cap_bytes = 512
+"#,
+    );
+
+    let err =
+        ProxyConfig::load(&path).expect_err("mask_shape_bucket_cap_bytes < floor must be rejected");
+    let msg = err.to_string();
+    assert!(
+        msg.contains(
+            "censorship.mask_shape_bucket_cap_bytes must be >= censorship.mask_shape_bucket_floor_bytes"
+        ),
+        "error must explain cap>=floor invariant, got: {msg}"
+    );
+
+    remove_temp_config(&path);
+}
+
+#[test]
+fn load_accepts_mask_shape_bucket_cap_equal_to_floor() {
+    let path = write_temp_config(
+        r#"
+[censorship]
+mask_shape_hardening = true
+mask_shape_bucket_floor_bytes = 1024
+mask_shape_bucket_cap_bytes = 1024
+"#,
+    );
+
+    let cfg = ProxyConfig::load(&path).expect("equal cap and floor must be accepted");
+    assert!(cfg.censorship.mask_shape_hardening);
+    assert_eq!(cfg.censorship.mask_shape_bucket_floor_bytes, 1024);
+    assert_eq!(cfg.censorship.mask_shape_bucket_cap_bytes, 1024);
+
+    remove_temp_config(&path);
+}
+
+#[test]
+fn load_rejects_above_cap_blur_when_shape_hardening_disabled() {
+    let path = write_temp_config(
+        r#"
+[censorship]
+mask_shape_hardening = false
+mask_shape_above_cap_blur = true
+mask_shape_above_cap_blur_max_bytes = 64
+"#,
+    );
+
+    let err = ProxyConfig::load(&path)
+        .expect_err("above-cap blur must require shape hardening enabled");
+    let msg = err.to_string();
+    assert!(
+        msg.contains("censorship.mask_shape_above_cap_blur requires censorship.mask_shape_hardening = true"),
+        "error must explain blur prerequisite, got: {msg}"
+    );
+
+    remove_temp_config(&path);
+}
+
+#[test]
+fn load_rejects_above_cap_blur_with_zero_max_bytes() {
+    let path = write_temp_config(
+        r#"
+[censorship]
+mask_shape_hardening = true
+mask_shape_above_cap_blur = true
+mask_shape_above_cap_blur_max_bytes = 0
+"#,
+    );
+
+    let err = ProxyConfig::load(&path)
+        .expect_err("above-cap blur max bytes must be > 0 when enabled");
+    let msg = err.to_string();
+    assert!(
+        msg.contains("censorship.mask_shape_above_cap_blur_max_bytes must be > 0 when censorship.mask_shape_above_cap_blur is enabled"),
+        "error must explain blur max bytes invariant, got: {msg}"
+    );
+
+    remove_temp_config(&path);
+}
+
+#[test]
+fn load_rejects_timing_normalization_floor_zero_when_enabled() {
+    let path = write_temp_config(
+        r#"
+[censorship]
+mask_timing_normalization_enabled = true
+mask_timing_normalization_floor_ms = 0
+mask_timing_normalization_ceiling_ms = 200
+"#,
+    );
+
+    let err = ProxyConfig::load(&path)
+        .expect_err("timing normalization floor must be > 0 when enabled");
+    let msg = err.to_string();
+    assert!(
+        msg.contains("censorship.mask_timing_normalization_floor_ms must be > 0 when censorship.mask_timing_normalization_enabled is true"),
+        "error must explain timing floor invariant, got: {msg}"
+    );
+
+    remove_temp_config(&path);
+}
+
+#[test]
+fn load_rejects_timing_normalization_ceiling_below_floor() {
+    let path = write_temp_config(
+        r#"
+[censorship]
+mask_timing_normalization_enabled = true
+mask_timing_normalization_floor_ms = 220
+mask_timing_normalization_ceiling_ms = 200
+"#,
+    );
+
+    let err = ProxyConfig::load(&path)
+        .expect_err("timing normalization ceiling must be >= floor");
+    let msg = err.to_string();
+    assert!(
+        msg.contains("censorship.mask_timing_normalization_ceiling_ms must be >= censorship.mask_timing_normalization_floor_ms"),
+        "error must explain timing ceiling/floor invariant, got: {msg}"
+    );
+
+    remove_temp_config(&path);
+}
+
+#[test]
+fn load_accepts_valid_timing_normalization_and_above_cap_blur_config() {
+    let path = write_temp_config(
+        r#"
+[censorship]
+mask_shape_hardening = true
+mask_shape_above_cap_blur = true
+mask_shape_above_cap_blur_max_bytes = 128
+mask_timing_normalization_enabled = true
+mask_timing_normalization_floor_ms = 150
+mask_timing_normalization_ceiling_ms = 240
+"#,
+    );
+
+    let cfg = ProxyConfig::load(&path)
+        .expect("valid blur and timing normalization settings must be accepted");
+    assert!(cfg.censorship.mask_shape_hardening);
+    assert!(cfg.censorship.mask_shape_above_cap_blur);
+    assert_eq!(cfg.censorship.mask_shape_above_cap_blur_max_bytes, 128);
+    assert!(cfg.censorship.mask_timing_normalization_enabled);
+    assert_eq!(cfg.censorship.mask_timing_normalization_floor_ms, 150);
+    assert_eq!(cfg.censorship.mask_timing_normalization_ceiling_ms, 240);
+
+    remove_temp_config(&path);
+}