Add ErrorKind::ShareParsingInvalidShareThreshold

Ensures that threshold > 2 during the parsing process, since we ensure the same
during the splitting process.

src/errors.rs

@@ -92,6 +92,11 @@ error_chain! {
             display("Found invalid share identifier ({})", share_id)
         }
 
+        ShareParsingInvalidShareThreshold(k: u8, id: u8) {
+            description("Threshold k must be bigger than or equal to 2")
+            display("Threshold k must be bigger than or equal to 2. Got k = {} for share identifier {}.", k, id)
+        }
+
         InvalidSS1Parameters(r: usize, s: usize) {
             description("Invalid parameters for the SS1 sharing scheme")
             display("Invalid parameters for the SS1 sharing scheme: r = {}, s = {}.", r, s)

src/share/validation.rs

@@ -39,6 +39,8 @@ pub(crate) fn validate_shares<S: IsShare>(shares: Vec<S>) -> Result<(u8, Vec<S>)
 
         if id < 1 {
             bail!(ErrorKind::ShareParsingInvalidShareId(id))
+        } else if threshold < 2 {
+            bail!(ErrorKind::ShareParsingInvalidShareThreshold(threshold, id))
         }
 
         k_compatibility_sets

tests/recovery_errors.rs

@@ -77,6 +77,17 @@ fn test_recover_too_few_shares() {
     recover_secret(&shares, false).unwrap();
 }
 
+#[test]
+#[should_panic(expected = "ShareParsingInvalidShareThreshold")]
+fn test_recover_invalid_share_threshold() {
+    let share1 = "1-1-CgnlCxRNtnkzENE".to_string();
+    let share2 = "1-1-CgkAnUgP3lfwjyM".to_string();
+
+    let shares = vec![share1, share2];
+
+    recover_secret(&shares, false).unwrap();
+}
+
 // See https://github.com/SpinResearch/RustySecrets/issues/43
 #[test]
 fn test_recover_too_few_shares_bug() {