diff --git a/crates/obscura-js/js/bootstrap.js b/crates/obscura-js/js/bootstrap.js
index 7db7e80..f364f54 100644
--- a/crates/obscura-js/js/bootstrap.js
+++ b/crates/obscura-js/js/bootstrap.js
@@ -6420,13 +6420,10 @@ if (!globalThis.crypto) globalThis.crypto = {};
 if (!globalThis.crypto.subtle) {
   globalThis.crypto.subtle = {
     async digest(algorithm, data) {
-      // Real WebCrypto digest. Delegates to `op_subtle_digest` which runs
-      // the actual SHA-1/256/384/512 via Rust's `sha1` and `sha2` crates.
-      // The previous JS implementation was a custom FNV variant that
-      // produced bytes shaped like the hash but with wrong contents, so
-      // SRI checks, JWS signature verification, and OAuth PKCE silently
-      // accepted invalid input.
-      const name = (typeof algorithm === 'string' ? algorithm : algorithm?.name) || 'SHA-256';
+      const name = (typeof algorithm === 'string' ? algorithm : algorithm?.name || '').toUpperCase().replace('_', '-');
+      if (name !== 'SHA-1' && name !== 'SHA-256' && name !== 'SHA-384' && name !== 'SHA-512') {
+        throw new DOMException('Unrecognized algorithm name', 'NotSupportedError');
+      }
       let bytes;
       if (data instanceof ArrayBuffer) bytes = new Uint8Array(data);
       else if (ArrayBuffer.isView(data)) bytes = new Uint8Array(data.buffer, data.byteOffset, data.byteLength);
diff --git a/crates/obscura-js/src/ops.rs b/crates/obscura-js/src/ops.rs
index bfbf1fd..6ae576b 100644
--- a/crates/obscura-js/src/ops.rs
+++ b/crates/obscura-js/src/ops.rs
@@ -1107,9 +1107,9 @@ fn op_binding_called(state: &OpState, #[string] name: &str, #[string] payload: &
 }
 
 /// Real WebCrypto `crypto.subtle.digest`. `algorithm` is the SubtleCrypto
-/// algorithm name (`SHA-1` / `SHA-256` / `SHA-384` / `SHA-512`); unknown
-/// names fall through to SHA-256 to match the previous JS fallback. Returns
-/// the raw digest bytes so the JS shim can hand them back as an ArrayBuffer.
+/// algorithm name (`SHA-1` / `SHA-256` / `SHA-384` / `SHA-512`). The JS shim
+/// validates the name before calling this op; any other value is unreachable.
+/// Returns the raw digest bytes so the JS shim can hand them back as an ArrayBuffer.
 #[op2]
 #[buffer]
 fn op_subtle_digest(#[string] algorithm: &str, #[buffer] data: &[u8]) -> Vec<u8> {
@@ -1120,7 +1120,7 @@ fn op_subtle_digest(#[string] algorithm: &str, #[buffer] data: &[u8]) -> Vec<u8>
         "SHA-256" => sha2::Sha256::digest(data).to_vec(),
         "SHA-384" => sha2::Sha384::digest(data).to_vec(),
         "SHA-512" => sha2::Sha512::digest(data).to_vec(),
-        _ => sha2::Sha256::digest(data).to_vec(),
+        _ => vec![],
     }
 }