rename the "context string" to the "purpose string"purpose_string

Apart from being pretty ambiguous in general, the term "context string"
has the specific problem that it isn't clear whether it should be
describing the input or the output. In fact, it's quite important that
it describes the output, because the whole point is to domain-separate
different outputs that derive from the *same* input. To make that
clearer, rename the "context string" to the "purpose string" in
documentation.

1 files changed, 11 insertions, 11 deletions

diff --git a/test_vectors/src/lib.rs b/test_vectors/src/lib.rs
index 129bd16..cc420c5 100644
--- a/test_vectors/src/lib.rs
+++ b/test_vectors/src/lib.rs
@@ -44,16 +44,16 @@ pub const TEST_CASES: &[usize] = &[
 ];
 
 pub const TEST_KEY: &[u8; blake3::KEY_LEN] = b"whats the Elvish word for friend";
-pub const TEST_CONTEXT: &str = "BLAKE3 2019-12-27 16:29:52 test vectors context";
+pub const TEST_PURPOSE: &str = "BLAKE3 2019-12-27 16:29:52 test vectors context";
 
 const COMMENT: &str = r#"
 Each test is an input length and three outputs, one for each of the hash,
 keyed_hash, and derive_key modes. The input in each case is filled with a
 repeating sequence of 251 bytes: 0, 1, 2, ..., 249, 250, 0, 1, ..., and so on.
 The key used with keyed_hash is the 32-byte ASCII string "whats the Elvish word
-for friend", also given in the `key` field below. The context string used with
+for friend", also given in the `key` field below. The purpose string used with
 derive_key is the ASCII string "BLAKE3 2019-12-27 16:29:52 test vectors
-context", also given in the `context_string` field below. Outputs are encoded
+context", also given in the `purpose_string` field below. Outputs are encoded
 as hexadecimal. Each case is an extended output, and implementations should
 also check that the first 32 bytes match their default-length output.
 "#;
@@ -72,7 +72,7 @@ pub fn paint_test_input(buf: &mut [u8]) {
 pub struct Cases {
     pub _comment: String,
     pub key: String,
-    pub context_string: String,
+    pub purpose_string: String,
     pub cases: Vec<Case>,
 }
 
@@ -103,7 +103,7 @@ pub fn generate_json() -> String {
             .fill(&mut keyed_hash_out);
 
         let mut derive_key_out = [0; OUTPUT_LEN];
-        blake3::Hasher::new_derive_key(TEST_CONTEXT)
+        blake3::Hasher::new_derive_key(TEST_PURPOSE)
             .update(&input)
             .finalize_xof()
             .fill(&mut derive_key_out);
@@ -119,7 +119,7 @@ pub fn generate_json() -> String {
     let mut json = serde_json::to_string_pretty(&Cases {
         _comment: COMMENT.trim().replace("\n", " "),
         key: std::str::from_utf8(TEST_KEY).unwrap().to_string(),
-        context_string: TEST_CONTEXT.to_string(),
+        purpose_string: TEST_PURPOSE.to_string(),
         cases,
     })
     .unwrap();
@@ -164,7 +164,7 @@ mod tests {
         assert_eq!(expected_keyed_hash, &out[..]);
 
         let mut out = vec![0; expected_derive_key.len()];
-        let mut hasher = reference_impl::Hasher::new_derive_key(TEST_CONTEXT);
+        let mut hasher = reference_impl::Hasher::new_derive_key(TEST_PURPOSE);
         hasher.update(input);
         hasher.finalize(&mut out);
         assert_eq!(expected_derive_key, &out[..]);
@@ -194,7 +194,7 @@ mod tests {
         assert_eq!(expected_keyed_hash, &out[..]);
 
         let mut out = vec![0; expected_derive_key.len()];
-        let mut hasher = reference_impl::Hasher::new_derive_key(TEST_CONTEXT);
+        let mut hasher = reference_impl::Hasher::new_derive_key(TEST_PURPOSE);
         for &b in input {
             hasher.update(&[b]);
         }
@@ -224,7 +224,7 @@ mod tests {
         assert_eq!(&expected_keyed_hash[..32], hasher.finalize().as_bytes());
 
         let mut out = vec![0; expected_derive_key.len()];
-        let mut hasher = blake3::Hasher::new_derive_key(TEST_CONTEXT);
+        let mut hasher = blake3::Hasher::new_derive_key(TEST_PURPOSE);
         hasher.update(input);
         hasher.finalize_xof().fill(&mut out);
         assert_eq!(expected_derive_key, &out[..]);
@@ -257,7 +257,7 @@ mod tests {
         assert_eq!(&expected_keyed_hash[..32], hasher.finalize().as_bytes());
 
         let mut out = vec![0; expected_derive_key.len()];
-        let mut hasher = blake3::Hasher::new_derive_key(TEST_CONTEXT);
+        let mut hasher = blake3::Hasher::new_derive_key(TEST_PURPOSE);
         for &b in input {
             hasher.update(&[b]);
         }
@@ -280,7 +280,7 @@ mod tests {
         );
         assert_eq!(
             expected_derive_key[..32],
-            blake3::derive_key(TEST_CONTEXT, input)
+            blake3::derive_key(TEST_PURPOSE, input)
         );
     }