feat(replication): SSE-C ciphertext passthrough replication (#5898)

Complete the encrypted-object replication series (backlog#1783, PR-C of
3, after #5872 and #5885): SSE-C objects replicate as ciphertext
passthrough — the source holds no customer key, so the stored bytes and
their encryption metadata travel verbatim and the replica decrypts only
with the original customer key, single-part and multipart.

- Sender: SSE-C objects read raw (raw_data_movement_read), transfer at
  ciphertext size, and range multipart parts over stored part sizes.
- Receiver: authorized replication PUTs restore the stored SSE-C keys
  from the transport headers (exact lowercase forms - the read-path
  check is case-sensitive), set ObjectOptions.preserve_ciphertext, and
  skip compression, bucket-default SSE, and sse_encryption behind one
  restore-derived gate. Multipart uses an internal session marker to
  store parts verbatim and strips it on complete.
- Convergence: the replication HEAD sends
  x-rustfs-source-replication-check; the target authorizes it as
  ReplicateObjectAction and skips SSE-C read validation for that
  request only, so keyless convergence HEADs see etag/size/mtime
  instead of 400 and SSE-C replicas stop re-driving forever.
- e2e: SSE-C contract flips to a key-gated readable replica (no-key and
  wrong-key GETs fail - the direct silent-plaintext detector); new
  multipart passthrough contract with ETag/marker/stability assertions.

rustfs/src/app/multipart_usecase.rs

@@ -81,7 +81,8 @@ use rustfs_s3_ops::S3Operation;
 use rustfs_targets::EventName;
 use rustfs_utils::CompressionAlgorithm;
 use rustfs_utils::http::{
-    SUFFIX_REPLICATION_STATUS, SUFFIX_REPLICATION_TIMESTAMP, get_source_scheme,
+    SUFFIX_REPLICATION_PRESERVE_CIPHERTEXT, SUFFIX_REPLICATION_STATUS, SUFFIX_REPLICATION_TIMESTAMP,
+    SUFFIX_SOURCE_REPLICATION_REQUEST, contains_key_str, get_header, get_source_scheme,
     headers::{AMZ_DECODED_CONTENT_LENGTH, AMZ_OBJECT_TAGGING, AMZ_STORAGE_CLASS},
     insert_str,
 };
@@ -504,19 +505,24 @@ impl DefaultMultipartUsecase {
             .get_multipart_info(&bucket, &key, &upload_id, &opts)
             .await
             .map_err(ApiError::from)?;
-        EncryptionRequest {
-            bucket: &bucket,
-            key: &key,
-            server_side_encryption: None,
-            ssekms_key_id: None,
-            ssekms_context: None,
-            sse_customer_algorithm,
-            sse_customer_key,
-            sse_customer_key_md5,
-            content_size: 0,
-            principal: None,
+        // A ciphertext-passthrough session stores encrypted parts verbatim and
+        // completes without the customer key (the replication client has none),
+        // so the SSE-C completion check must be skipped for it.
+        if !contains_key_str(&multipart_info.user_defined, SUFFIX_REPLICATION_PRESERVE_CIPHERTEXT) {
+            EncryptionRequest {
+                bucket: &bucket,
+                key: &key,
+                server_side_encryption: None,
+                ssekms_key_id: None,
+                ssekms_context: None,
+                sse_customer_algorithm,
+                sse_customer_key,
+                sse_customer_key_md5,
+                content_size: 0,
+                principal: None,
+            }
+            .validate_multipart_ssec(&multipart_info.user_defined)?;
         }
-        .validate_multipart_ssec(&multipart_info.user_defined)?;
         let cache_adapter = self.object_data_cache();
         let _ = invalidate_object_data_cache_before_mutation(&cache_adapter, &bucket, &key).await;
 
@@ -759,7 +765,22 @@ impl DefaultMultipartUsecase {
             principal: session_principal.as_ref(),
         };
 
-        let (effective_sse, effective_kms_key_id) = match sse_prepare_encryption(encryption_request).await? {
+        // SSE-C ciphertext passthrough: parts are already encrypted, so no
+        // session DEK is prepared; a session marker tells UploadPart to store
+        // the ciphertext verbatim instead of recovering encryption material.
+        let ciphertext_passthrough = replication_authorized
+            && get_header(&req.headers, SUFFIX_SOURCE_REPLICATION_REQUEST).as_deref() == Some("true")
+            && rustfs_utils::http::ssec_transport_to_stored_metadata(&req.headers).is_some();
+        if ciphertext_passthrough {
+            insert_str(&mut metadata, SUFFIX_REPLICATION_PRESERVE_CIPHERTEXT, "true".to_string());
+        }
+
+        let prepared_material = if ciphertext_passthrough {
+            None
+        } else {
+            sse_prepare_encryption(encryption_request).await?
+        };
+        let (effective_sse, effective_kms_key_id) = match prepared_material {
             Some(material) => {
                 let server_side_encryption = Some(material.server_side_encryption.clone());
                 let ssekms_key_id = material.kms_key_id.clone();
@@ -951,10 +972,14 @@ impl DefaultMultipartUsecase {
         }
         opts.want_checksum = reader.checksum();
 
-        let has_ssec = fi
-            .user_defined
-            .contains_key("x-amz-server-side-encryption-customer-algorithm");
-        let (server_side_encryption, ssekms_key_id) = if has_ssec {
+        // An SSE-C passthrough session stores ciphertext parts verbatim: no
+        // material recovery, no validation against the (absent) customer key.
+        let preserve_ciphertext = contains_key_str(&fi.user_defined, SUFFIX_REPLICATION_PRESERVE_CIPHERTEXT);
+        let has_ssec = !preserve_ciphertext
+            && fi
+                .user_defined
+                .contains_key("x-amz-server-side-encryption-customer-algorithm");
+        let (server_side_encryption, ssekms_key_id) = if has_ssec || preserve_ciphertext {
             (None, None)
         } else {
             let sse = fi
@@ -974,19 +999,21 @@ impl DefaultMultipartUsecase {
             };
             (sse, key_id)
         };
-        EncryptionRequest {
-            bucket: &bucket,
-            key: &key,
-            server_side_encryption: server_side_encryption.clone(),
-            ssekms_key_id: ssekms_key_id.clone(),
-            ssekms_context: None,
-            sse_customer_algorithm: sse_customer_algorithm.clone(),
-            sse_customer_key: sse_customer_key.clone(),
-            sse_customer_key_md5: sse_customer_key_md5.clone(),
-            content_size: actual_size,
-            principal: None,
+        if !preserve_ciphertext {
+            EncryptionRequest {
+                bucket: &bucket,
+                key: &key,
+                server_side_encryption: server_side_encryption.clone(),
+                ssekms_key_id: ssekms_key_id.clone(),
+                ssekms_context: None,
+                sse_customer_algorithm: sse_customer_algorithm.clone(),
+                sse_customer_key: sse_customer_key.clone(),
+                sse_customer_key_md5: sse_customer_key_md5.clone(),
+                content_size: actual_size,
+                principal: None,
+            }
+            .validate_multipart_ssec(&fi.user_defined)?;
         }
-        .validate_multipart_ssec(&fi.user_defined)?;
         let (requested_sse, requested_kms_key_id) = if has_ssec {
             let ssec_material = sse_decryption(DecryptionRequest {
                 bucket: &bucket,

rustfs/src/app/object_usecase.rs

@@ -137,8 +137,8 @@ use rustfs_utils::CompressionAlgorithm;
 use rustfs_utils::http::{
     AMZ_BUCKET_REPLICATION_STATUS, AMZ_CHECKSUM_MODE, AMZ_CHECKSUM_TYPE, AMZ_WEBSITE_REDIRECT_LOCATION, CONTENT_TYPE,
     SUFFIX_ACTUAL_SIZE, SUFFIX_COMPRESSION, SUFFIX_COMPRESSION_SIZE, SUFFIX_REPLICA_STATUS, SUFFIX_REPLICA_TIMESTAMP,
-    SUFFIX_REPLICATION_STATUS, SUFFIX_REPLICATION_TIMESTAMP, SUFFIX_RESTORE_OPERATION_ID, SUFFIX_SOURCE_REPLICATION_REQUEST,
-    get_header,
+    SUFFIX_REPLICATION_STATUS, SUFFIX_REPLICATION_TIMESTAMP, SUFFIX_RESTORE_OPERATION_ID, SUFFIX_SOURCE_REPLICATION_CHECK,
+    SUFFIX_SOURCE_REPLICATION_REQUEST, get_header,
     headers::{
         AMZ_CONTENT_SHA256, AMZ_DECODED_CONTENT_LENGTH, AMZ_MINIO_SNOWBALL_IGNORE_DIRS, AMZ_MINIO_SNOWBALL_IGNORE_ERRORS,
         AMZ_MINIO_SNOWBALL_PREFIX, AMZ_OBJECT_LOCK_LEGAL_HOLD, AMZ_OBJECT_LOCK_LEGAL_HOLD_LOWER, AMZ_OBJECT_LOCK_MODE,
@@ -5393,6 +5393,11 @@ impl DefaultObjectUsecase {
         if is_put_object_extract_requested(&req.headers) && !inbound_replication_put {
             return Box::pin(self.execute_put_object_extract(req)).await;
         }
+        // SSE-C ciphertext passthrough (authorized replication only): the body
+        // is already ciphertext and must be stored verbatim — no compression,
+        // no bucket-default encryption.
+        let ciphertext_passthrough =
+            inbound_replication_put && rustfs_utils::http::ssec_transport_to_stored_metadata(&req.headers).is_some();
 
         let input = std::mem::take(&mut req.input);
 
@@ -5465,7 +5470,8 @@ impl DefaultObjectUsecase {
         self.check_bucket_quota(&bucket, quota_operation, size as u64).await?;
 
         let ingress_stage_start = std::time::Instant::now();
-        let should_compress = is_disk_compressible(&req.headers, &key) && size > MIN_DISK_COMPRESSIBLE_SIZE as i64;
+        let should_compress =
+            is_disk_compressible(&req.headers, &key) && size > MIN_DISK_COMPRESSIBLE_SIZE as i64 && !ciphertext_passthrough;
         let server_side_encryption_requested =
             server_side_encryption.is_some() || sse_customer_algorithm.is_some() || ssekms_key_id.is_some();
 
@@ -5575,6 +5581,13 @@ impl DefaultObjectUsecase {
             })
         });
 
+        if ciphertext_passthrough {
+            // The replica keeps the source's SSE-C metadata; the bucket
+            // default must not claim managed encryption on it.
+            effective_sse = None;
+            effective_kms_key_id = None;
+        }
+
         // Validate SSE-C headers early: reject partial/invalid combinations per S3 spec
         validate_sse_headers_for_write(
             effective_sse.as_ref(),
@@ -5778,12 +5791,20 @@ impl DefaultObjectUsecase {
             principal: write_principal.as_ref(),
         };
 
-        let encryption_material = match sse_encryption(encryption_request).await {
-            Ok(material) => material,
-            Err(err) => {
-                let result = Err(err.into());
-                let _ = helper.complete(&result);
-                return result;
+        // SSE-C ciphertext passthrough must skip sse_encryption entirely: an
+        // explicit guard is required because prepare_sse_configuration inside
+        // it falls back to the bucket default encryption config and would
+        // double-encrypt the already-encrypted body.
+        let encryption_material = if opts.preserve_ciphertext {
+            None
+        } else {
+            match sse_encryption(encryption_request).await {
+                Ok(material) => material,
+                Err(err) => {
+                    let result = Err(err.into());
+                    let _ = helper.complete(&result);
+                    return result;
+                }
             }
         };
 
@@ -8319,15 +8340,22 @@ impl DefaultObjectUsecase {
         {
             return Err(S3Error::new(S3ErrorCode::PreconditionFailed));
         }
-        validate_sse_headers_for_read(&info.user_defined, &req.headers)?;
+        // An authorized replication convergence check only needs etag/size/mtime
+        // to compare source and replica; it holds no customer key, so the SSE-C
+        // read validation is skipped for it (and only it).
+        let replication_check = replication_request_authorized(&req)
+            && get_header(&req.headers, SUFFIX_SOURCE_REPLICATION_CHECK).as_deref() == Some("true");
+        if !replication_check {
+            validate_sse_headers_for_read(&info.user_defined, &req.headers)?;
 
-        // Validate SSE-C: if the object was encrypted with a customer-provided key,
-        // the caller must supply the matching key even for HEAD requests (per S3 spec).
-        validate_ssec_for_read(
-            &info.user_defined,
-            req.input.sse_customer_key.as_ref(),
-            req.input.sse_customer_key_md5.as_ref(),
-        )?;
+            // Validate SSE-C: if the object was encrypted with a customer-provided key,
+            // the caller must supply the matching key even for HEAD requests (per S3 spec).
+            validate_ssec_for_read(
+                &info.user_defined,
+                req.input.sse_customer_key.as_ref(),
+                req.input.sse_customer_key_md5.as_ref(),
+            )?;
+        }
 
         // Compute x-amz-expiration header from lifecycle prediction (before info is partially moved)
         let expiration_header = resolve_put_object_expiration(&bucket, &info).await;

rustfs/src/storage/access.rs

@@ -87,6 +87,7 @@ fn has_replication_only_put_headers(headers: &HeaderMap) -> bool {
         || get_header(headers, SUFFIX_SOURCE_REPLICATION_CHECK).is_some()
         || get_header(headers, SUFFIX_SOURCE_REPLICATION_REQUEST).is_some()
         || get_header(headers, SUFFIX_SOURCE_VERSION_ID).is_some()
+        || rustfs_utils::http::has_ssec_transport_headers(headers)
 }
 
 async fn authorize_replication_only_put_headers<T>(req: &mut S3Request<T>) -> S3Result<()> {
@@ -2182,6 +2183,16 @@ impl S3Access for FS {
         req_info.object = Some(req.input.key.clone());
         req_info.version_id = req.input.version_id.clone();
 
+        // A replication convergence check HEADs the replica to compare
+        // etag/size/mtime. For SSE-C replicas the worker holds no customer key,
+        // so authorize it as a replication action and let the handler skip the
+        // SSE-C read validation.
+        if get_header(&req.headers, SUFFIX_SOURCE_REPLICATION_CHECK).as_deref() == Some("true") {
+            authorize_request(req, Action::S3Action(S3Action::ReplicateObjectAction)).await?;
+            req_info_mut(req)?.replication_request_authorized = true;
+            return Ok(());
+        }
+
         authorize_request(req, Action::S3Action(S3Action::GetObjectAction)).await
     }
 

rustfs/src/storage/options.rs

@@ -427,6 +427,16 @@ pub fn put_opts_from_headers_with_replication_authorization(
         opts.replication_request = true;
         opts.mod_time = replication_source_mtime(headers);
         opts.preserve_etag = replication_source_etag(headers);
+        // SSE-C ciphertext passthrough: restore the stored encryption metadata
+        // from the transport headers and mark the body as already encrypted so
+        // the write path stores it verbatim.
+        if let Some(restored) = rustfs_utils::http::ssec_transport_to_stored_metadata(headers) {
+            opts.user_defined.extend(restored);
+            opts.preserve_ciphertext = true;
+        }
+        if let Some(crc) = get_header(headers, SUFFIX_REPLICATION_SSEC_CRC) {
+            insert_header_map(&mut opts.user_defined, SUFFIX_REPLICATION_SSEC_CRC, crc.into_owned());
+        }
     }
     Ok(opts)
 }
@@ -1470,6 +1480,56 @@ mod tests {
         assert!(opts.preserve_etag.is_none());
     }
 
+    #[test]
+    fn test_put_opts_from_headers_gates_ssec_passthrough_on_authorization() {
+        use rustfs_utils::http::object_encryption_keys::{
+            INTERNAL_ENCRYPTION_IV_HEADER, REPLICATION_ENCRYPTION_IV_HEADER, REPLICATION_SSEC_ALGORITHM_HEADER,
+        };
+
+        let mut headers = HeaderMap::new();
+        insert_header(&mut headers, SUFFIX_SOURCE_REPLICATION_REQUEST, "true");
+        headers.insert(
+            REPLICATION_SSEC_ALGORITHM_HEADER.parse::<http::HeaderName>().unwrap(),
+            HeaderValue::from_static("AES256"),
+        );
+        headers.insert(
+            REPLICATION_ENCRYPTION_IV_HEADER.parse::<http::HeaderName>().unwrap(),
+            HeaderValue::from_static("iv-value"),
+        );
+
+        // Unauthorized: the transport headers must be inert — no restored
+        // encryption metadata, no ciphertext-passthrough flag.
+        let untrusted = put_opts_from_headers(&headers, HashMap::new()).expect("ordinary PUT options should be created");
+        assert!(!untrusted.preserve_ciphertext);
+        assert!(!untrusted.user_defined.contains_key(INTERNAL_ENCRYPTION_IV_HEADER));
+        assert!(
+            !untrusted
+                .user_defined
+                .contains_key("x-amz-server-side-encryption-customer-algorithm")
+        );
+
+        // Authorized: the stored keys are restored and the write path is told
+        // the body is already ciphertext.
+        let trusted = put_opts_from_headers_with_replication_authorization(&headers, HashMap::new(), true)
+            .expect("authorized replication request should parse");
+        assert!(trusted.preserve_ciphertext);
+        assert_eq!(
+            trusted.user_defined.get(INTERNAL_ENCRYPTION_IV_HEADER).map(String::as_str),
+            Some("iv-value")
+        );
+        assert_eq!(
+            trusted
+                .user_defined
+                .get("x-amz-server-side-encryption-customer-algorithm")
+                .map(String::as_str),
+            Some("AES256")
+        );
+        assert_eq!(
+            trusted.user_defined.get("x-amz-server-side-encryption").map(String::as_str),
+            Some("AES256")
+        );
+    }
+
     #[test]
     fn test_put_opts_from_headers_accepts_replication_request_after_authorization() {
         let mut headers = HeaderMap::new();