diff --git a/crates/s3-client/src/api_get_object.rs b/crates/s3-client/src/api_get_object.rs
index 9f6f49d59..cc06fe388 100644
--- a/crates/s3-client/src/api_get_object.rs
+++ b/crates/s3-client/src/api_get_object.rs
@@ -69,7 +69,6 @@ impl TransitionClient {
                     stream_sha256: false,
                     trailer: HeaderMap::new(),
                     pre_sign_url: Default::default(),
-                    add_crc: Default::default(),
                     extra_pre_sign_header: Default::default(),
                     bucket_location: Default::default(),
                     expires: Default::default(),
diff --git a/crates/s3-client/src/api_list.rs b/crates/s3-client/src/api_list.rs
index 3bd1f1edd..c2771d081 100644
--- a/crates/s3-client/src/api_list.rs
+++ b/crates/s3-client/src/api_list.rs
@@ -103,7 +103,6 @@ impl TransitionClient {
                     stream_sha256: false,
                     trailer: HeaderMap::new(),
                     pre_sign_url: Default::default(),
-                    add_crc: Default::default(),
                     extra_pre_sign_header: Default::default(),
                     bucket_location: Default::default(),
                     expires: Default::default(),
@@ -206,7 +205,6 @@ impl TransitionClient {
                     stream_sha256: false,
                     trailer: HeaderMap::new(),
                     pre_sign_url: Default::default(),
-                    add_crc: Default::default(),
                     extra_pre_sign_header: Default::default(),
                     bucket_location: Default::default(),
                     expires: Default::default(),
diff --git a/crates/s3-client/src/api_put_object_multipart.rs b/crates/s3-client/src/api_put_object_multipart.rs
index 17efdbf3a..d7d1ba7a1 100644
--- a/crates/s3-client/src/api_put_object_multipart.rs
+++ b/crates/s3-client/src/api_put_object_multipart.rs
@@ -26,7 +26,7 @@ use time::OffsetDateTime;
 use tracing::warn;
 use uuid::Uuid;
 
-use crate::checksum::ChecksumMode;
+use crate::checksum::{ChecksumMode, checksum_header_value};
 use crate::utils::base64_encode;
 use crate::{
     api_error_response::{
@@ -223,7 +223,6 @@ impl TransitionClient {
             stream_sha256: false,
             trailer: HeaderMap::new(),
             pre_sign_url: Default::default(),
-            add_crc: Default::default(),
             extra_pre_sign_header: Default::default(),
             bucket_location: Default::default(),
             expires: Default::default(),
@@ -306,7 +305,6 @@ impl TransitionClient {
             stream_sha256: p.stream_sha256,
             trailer: p.trailer.clone(),
             pre_sign_url: Default::default(),
-            add_crc: Default::default(),
             extra_pre_sign_header: Default::default(),
             bucket_location: Default::default(),
             expires: Default::default(),
@@ -329,31 +327,11 @@ impl TransitionClient {
         //}
         let h = resp.headers();
         let mut obj_part = ObjectPart {
-            checksum_crc32: if let Some(h_checksum_crc32) = h.get(ChecksumMode::ChecksumCRC32.key()) {
-                h_checksum_crc32.to_str().unwrap_or("").to_string()
-            } else {
-                "".to_string()
-            },
-            checksum_crc32c: if let Some(h_checksum_crc32c) = h.get(ChecksumMode::ChecksumCRC32C.key()) {
-                h_checksum_crc32c.to_str().unwrap_or("").to_string()
-            } else {
-                "".to_string()
-            },
-            checksum_sha1: if let Some(h_checksum_sha1) = h.get(ChecksumMode::ChecksumSHA1.key()) {
-                h_checksum_sha1.to_str().unwrap_or("").to_string()
-            } else {
-                "".to_string()
-            },
-            checksum_sha256: if let Some(h_checksum_sha256) = h.get(ChecksumMode::ChecksumSHA256.key()) {
-                h_checksum_sha256.to_str().unwrap_or("").to_string()
-            } else {
-                "".to_string()
-            },
-            checksum_crc64nvme: if let Some(h_checksum_crc64nvme) = h.get(ChecksumMode::ChecksumCRC64NVME.key()) {
-                h_checksum_crc64nvme.to_str().unwrap_or("").to_string()
-            } else {
-                "".to_string()
-            },
+            checksum_crc32: checksum_header_value(h, ChecksumMode::ChecksumCRC32),
+            checksum_crc32c: checksum_header_value(h, ChecksumMode::ChecksumCRC32C),
+            checksum_sha1: checksum_header_value(h, ChecksumMode::ChecksumSHA1),
+            checksum_sha256: checksum_header_value(h, ChecksumMode::ChecksumSHA256),
+            checksum_crc64nvme: checksum_header_value(h, ChecksumMode::ChecksumCRC64NVME),
             ..Default::default()
         };
         obj_part.size = p.size;
@@ -393,7 +371,6 @@ impl TransitionClient {
             stream_sha256: Default::default(),
             trailer: Default::default(),
             pre_sign_url: Default::default(),
-            add_crc: Default::default(),
             extra_pre_sign_header: Default::default(),
             bucket_location: Default::default(),
             expires: Default::default(),
diff --git a/crates/s3-client/src/api_put_object_streaming.rs b/crates/s3-client/src/api_put_object_streaming.rs
index 9ae54b893..8c9c7b5a1 100644
--- a/crates/s3-client/src/api_put_object_streaming.rs
+++ b/crates/s3-client/src/api_put_object_streaming.rs
@@ -31,7 +31,7 @@ use tokio_util::sync::CancellationToken;
 use tracing::warn;
 use uuid::Uuid;
 
-use crate::checksum::{ChecksumMode, add_auto_checksum_headers, apply_auto_checksum};
+use crate::checksum::{ChecksumMode, add_auto_checksum_headers, apply_auto_checksum, checksum_header_value};
 use crate::{
     api_error_response::{err_invalid_argument, err_unexpected_eof, http_resp_to_error_response},
     api_put_object::PutObjectOptions,
@@ -503,7 +503,6 @@ impl TransitionClient {
             content_md5_base64: md5_base64.to_string(),
             content_sha256_hex: sha256_hex.to_string(),
             stream_sha256: !opts.disable_content_sha256,
-            add_crc: Default::default(),
             bucket_location: Default::default(),
             pre_sign_url: Default::default(),
             query_values: Default::default(),
@@ -511,21 +510,7 @@ impl TransitionClient {
             expires: Default::default(),
             trailer: Default::default(),
         };
-        let mut add_crc = false; //self.trailing_header_support && md5_base64 == "" && !s3utils.IsGoogleEndpoint(self.endpoint_url) && (opts.disable_content_sha256 || self.secure);
-        let mut opts = opts.clone();
-        if opts.checksum.is_set() {
-            req_metadata.add_crc = opts.checksum;
-        } else if add_crc {
-            for (k, _) in opts.user_metadata {
-                if k.to_lowercase().starts_with("x-amz-checksum-") {
-                    add_crc = false;
-                }
-            }
-            if add_crc {
-                opts.auto_checksum.set_default(ChecksumMode::ChecksumCRC32C);
-                req_metadata.add_crc = opts.auto_checksum;
-            }
-        }
+        let opts = opts.clone();
 
         if opts.internal.source_version_id != "" {
             if !opts.internal.source_version_id.is_empty() {
@@ -570,31 +555,11 @@ impl TransitionClient {
             size,
             expiration: exp_time,
             expiration_rule_id: rule_id,
-            checksum_crc32: if let Some(h_checksum_crc32) = h.get(ChecksumMode::ChecksumCRC32.key()) {
-                h_checksum_crc32.to_str().unwrap_or("").to_string()
-            } else {
-                "".to_string()
-            },
-            checksum_crc32c: if let Some(h_checksum_crc32c) = h.get(ChecksumMode::ChecksumCRC32C.key()) {
-                h_checksum_crc32c.to_str().unwrap_or("").to_string()
-            } else {
-                "".to_string()
-            },
-            checksum_sha1: if let Some(h_checksum_sha1) = h.get(ChecksumMode::ChecksumSHA1.key()) {
-                h_checksum_sha1.to_str().unwrap_or("").to_string()
-            } else {
-                "".to_string()
-            },
-            checksum_sha256: if let Some(h_checksum_sha256) = h.get(ChecksumMode::ChecksumSHA256.key()) {
-                h_checksum_sha256.to_str().unwrap_or("").to_string()
-            } else {
-                "".to_string()
-            },
-            checksum_crc64nvme: if let Some(h_checksum_crc64nvme) = h.get(ChecksumMode::ChecksumCRC64NVME.key()) {
-                h_checksum_crc64nvme.to_str().unwrap_or("").to_string()
-            } else {
-                "".to_string()
-            },
+            checksum_crc32: checksum_header_value(h, ChecksumMode::ChecksumCRC32),
+            checksum_crc32c: checksum_header_value(h, ChecksumMode::ChecksumCRC32C),
+            checksum_sha1: checksum_header_value(h, ChecksumMode::ChecksumSHA1),
+            checksum_sha256: checksum_header_value(h, ChecksumMode::ChecksumSHA256),
+            checksum_crc64nvme: checksum_header_value(h, ChecksumMode::ChecksumCRC64NVME),
             ..Default::default()
         })
     }
diff --git a/crates/s3-client/src/api_remove.rs b/crates/s3-client/src/api_remove.rs
index 3002e71ca..5e063e14f 100644
--- a/crates/s3-client/src/api_remove.rs
+++ b/crates/s3-client/src/api_remove.rs
@@ -99,7 +99,6 @@ impl TransitionClient {
                     stream_sha256: false,
                     trailer: HeaderMap::new(),
                     pre_sign_url: Default::default(),
-                    add_crc: Default::default(),
                     extra_pre_sign_header: Default::default(),
                     bucket_location: Default::default(),
                     expires: Default::default(),
@@ -131,7 +130,6 @@ impl TransitionClient {
                     stream_sha256: false,
                     trailer: HeaderMap::new(),
                     pre_sign_url: Default::default(),
-                    add_crc: Default::default(),
                     extra_pre_sign_header: Default::default(),
                     bucket_location: Default::default(),
                     expires: Default::default(),
@@ -185,7 +183,6 @@ impl TransitionClient {
                     stream_sha256: false,
                     trailer: HeaderMap::new(),
                     pre_sign_url: Default::default(),
-                    add_crc: Default::default(),
                     extra_pre_sign_header: Default::default(),
                     bucket_location: Default::default(),
                     expires: Default::default(),
@@ -347,7 +344,6 @@ impl TransitionClient {
                         stream_sha256: false,
                         trailer: HeaderMap::new(),
                         pre_sign_url: Default::default(),
-                        add_crc: Default::default(),
                         extra_pre_sign_header: Default::default(),
                         bucket_location: Default::default(),
                         expires: Default::default(),
@@ -407,7 +403,6 @@ impl TransitionClient {
                     stream_sha256: false,
                     trailer: HeaderMap::new(),
                     pre_sign_url: Default::default(),
-                    add_crc: Default::default(),
                     extra_pre_sign_header: Default::default(),
                     bucket_location: Default::default(),
                     expires: Default::default(),
diff --git a/crates/s3-client/src/api_s3_datatypes.rs b/crates/s3-client/src/api_s3_datatypes.rs
index 2f6475815..d17eb6cbb 100644
--- a/crates/s3-client/src/api_s3_datatypes.rs
+++ b/crates/s3-client/src/api_s3_datatypes.rs
@@ -262,32 +262,6 @@ pub struct CompletePart {
     pub checksum_crc64nvme: String,
 }
 
-impl CompletePart {
-    #[allow(dead_code, reason = "MinIO-parity accessor with no caller in this port (backlog#1823)")]
-    fn checksum(&self, t: &ChecksumMode) -> String {
-        match t {
-            ChecksumMode::ChecksumCRC32C => {
-                return self.checksum_crc32c.clone();
-            }
-            ChecksumMode::ChecksumCRC32 => {
-                return self.checksum_crc32.clone();
-            }
-            ChecksumMode::ChecksumSHA1 => {
-                return self.checksum_sha1.clone();
-            }
-            ChecksumMode::ChecksumSHA256 => {
-                return self.checksum_sha256.clone();
-            }
-            ChecksumMode::ChecksumCRC64NVME => {
-                return self.checksum_crc64nvme.clone();
-            }
-            _ => {
-                return "".to_string();
-            }
-        }
-    }
-}
-
 #[derive(Debug, Default, serde::Serialize)]
 #[serde(rename = "CompleteMultipartUpload")]
 pub struct CompleteMultipartUpload {
diff --git a/crates/s3-client/src/api_stat.rs b/crates/s3-client/src/api_stat.rs
index c4bc8c9d8..bac59c8ed 100644
--- a/crates/s3-client/src/api_stat.rs
+++ b/crates/s3-client/src/api_stat.rs
@@ -104,7 +104,6 @@ impl TransitionClient {
                     stream_sha256: false,
                     trailer: HeaderMap::new(),
                     pre_sign_url: Default::default(),
-                    add_crc: Default::default(),
                     extra_pre_sign_header: Default::default(),
                     bucket_location: Default::default(),
                     expires: Default::default(),
@@ -159,7 +158,6 @@ impl TransitionClient {
                     stream_sha256: false,
                     trailer: HeaderMap::new(),
                     pre_sign_url: Default::default(),
-                    add_crc: Default::default(),
                     extra_pre_sign_header: Default::default(),
                     bucket_location: Default::default(),
                     expires: Default::default(),
@@ -212,7 +210,6 @@ impl TransitionClient {
                     stream_sha256: false,
                     trailer: HeaderMap::new(),
                     pre_sign_url: Default::default(),
-                    add_crc: Default::default(),
                     extra_pre_sign_header: Default::default(),
                     bucket_location: Default::default(),
                     expires: Default::default(),
diff --git a/crates/s3-client/src/checksum.rs b/crates/s3-client/src/checksum.rs
index b85abb06b..06aacdb06 100644
--- a/crates/s3-client/src/checksum.rs
+++ b/crates/s3-client/src/checksum.rs
@@ -1,4 +1,3 @@
-#![allow(clippy::map_entry)]
 // Copyright 2024 RustFS Team
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
@@ -12,17 +11,10 @@
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-#![allow(unused_imports)]
-#![allow(unused_variables)]
-#![allow(unused_mut)]
-#![allow(unused_assignments)]
-#![allow(unused_must_use)]
-#![allow(clippy::all)]
 
 use rustfs_checksums::ChecksumAlgorithm;
 use std::collections::HashMap;
 
-use crate::utils::base64_decode;
 use crate::utils::base64_encode;
 use crate::{api_put_object::PutObjectOptions, api_s3_datatypes::ObjectPart};
 
@@ -104,10 +96,6 @@ impl ChecksumMode {
             .is_some_and(|a| a.supports_full_object() && !a.supports_composite())
     }
 
-    pub fn key_capitalized(&self) -> String {
-        self.key()
-    }
-
     pub fn raw_byte_len(&self) -> usize {
         self.algorithm().map(|a| a.raw_len()).unwrap_or(0)
     }
@@ -144,39 +132,13 @@ impl ChecksumMode {
         Ok(base64_encode(hash.as_ref()))
     }
 
-    pub fn to_string(&self) -> String {
-        match self.algorithm() {
-            Some(algorithm) => algorithm.s3_algorithm_name().to_string(),
-            None if matches!(self, ChecksumMode::ChecksumNone) => "".to_string(),
-            None => "<invalid>".to_string(),
-        }
-    }
-
-    // pub fn check_sum_reader(&self, r: GetObjectReader) -> Result<Checksum, std::io::Error> {
-    //     let mut h = self.hasher()?;
-    //     Ok(Checksum::new(self.clone(), h.sum().as_bytes()))
-    // }
-
-    // pub fn check_sum_bytes(&self, b: &[u8]) -> Result<Checksum, std::io::Error> {
-    //     let mut h = self.hasher()?;
-    //     Ok(Checksum::new(self.clone(), h.sum().as_bytes()))
-    // }
-
     pub fn composite_checksum(&self, p: &mut [ObjectPart]) -> Result<Checksum, std::io::Error> {
         if !self.can_composite() {
             return Err(std::io::Error::other("cannot do composite checksum"));
         }
-        p.sort_by(|i, j| {
-            if i.part_num < j.part_num {
-                std::cmp::Ordering::Less
-            } else if i.part_num > j.part_num {
-                std::cmp::Ordering::Greater
-            } else {
-                std::cmp::Ordering::Equal
-            }
-        });
+        p.sort_by_key(|part| part.part_num);
         let c = self.base();
-        let mut crc_bytes = Vec::<u8>::with_capacity(p.len() * self.raw_byte_len() as usize);
+        let mut crc_bytes = Vec::<u8>::with_capacity(p.len() * self.raw_byte_len());
         let mut h = self.hasher()?;
         for part in p.iter() {
             let part_checksum = part.checksum_raw(&c)?;
@@ -185,9 +147,8 @@ impl ChecksumMode {
         h.update(crc_bytes.as_ref());
         let hash = h.finalize();
         Ok(Checksum {
-            checksum_type: self.clone(),
+            checksum_type: *self,
             r: hash.as_ref().to_vec(),
-            computed: false,
         })
     }
 
@@ -200,6 +161,19 @@ impl ChecksumMode {
     }
 }
 
+impl std::fmt::Display for ChecksumMode {
+    /// The `x-amz-checksum-algorithm` wire value: the algorithm name for
+    /// concrete modes, `""` for `ChecksumNone`, `"<invalid>"` for a bare
+    /// `ChecksumFullObject` flag.
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self.algorithm() {
+            Some(algorithm) => f.write_str(algorithm.s3_algorithm_name()),
+            None if matches!(self, ChecksumMode::ChecksumNone) => Ok(()),
+            None => f.write_str("<invalid>"),
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::ChecksumMode;
@@ -332,7 +306,6 @@ mod tests {
 
         for e in table {
             assert_eq!(e.mode.key(), e.key, "{:?} key()", e.mode);
-            assert_eq!(e.mode.key_capitalized(), e.key, "{:?} key_capitalized()", e.mode);
             assert_eq!(e.mode.to_string(), e.name, "{:?} to_string()", e.mode);
             assert_eq!(e.mode.raw_byte_len(), e.raw_len, "{:?} raw_byte_len()", e.mode);
             assert_eq!(e.mode.can_composite(), e.composite, "{:?} can_composite()", e.mode);
@@ -351,6 +324,24 @@ mod tests {
         }
     }
 
+    #[test]
+    fn test_checksum_header_value_reads_present_absent_and_invalid() {
+        use super::checksum_header_value;
+        use http::{HeaderMap, HeaderValue};
+
+        let mut headers = HeaderMap::new();
+        headers.insert("x-amz-checksum-crc32c", HeaderValue::from_static("yZRlqg=="));
+        headers.insert("x-amz-checksum-sha256", HeaderValue::from_bytes(b"\xff\xfe").unwrap());
+
+        // Present header returns its value verbatim.
+        assert_eq!(checksum_header_value(&headers, ChecksumMode::ChecksumCRC32C), "yZRlqg==");
+        // Absent header and the unset modes (whose key() is "") return "".
+        assert_eq!(checksum_header_value(&headers, ChecksumMode::ChecksumCRC32), "");
+        assert_eq!(checksum_header_value(&headers, ChecksumMode::ChecksumNone), "");
+        // A non-UTF-8 header value degrades to "" instead of erroring.
+        assert_eq!(checksum_header_value(&headers, ChecksumMode::ChecksumSHA256), "");
+    }
+
     #[test]
     fn test_set_default_upgrades_none() {
         // With `is_set()` fixed, `set_default` must upgrade an unset mode to the
@@ -371,42 +362,9 @@ mod tests {
 pub struct Checksum {
     checksum_type: ChecksumMode,
     r: Vec<u8>,
-    #[allow(
-        dead_code,
-        reason = "checksum bookkeeping field kept beside the value it guards (backlog#1823)"
-    )]
-    computed: bool,
 }
 
 impl Checksum {
-    #[allow(dead_code, reason = "MinIO-parity surface with no caller in this port (backlog#1823)")]
-    fn new(t: ChecksumMode, b: &[u8]) -> Checksum {
-        if t.is_set() && b.len() == t.raw_byte_len() {
-            return Checksum {
-                checksum_type: t,
-                r: b.to_vec(),
-                computed: false,
-            };
-        }
-        Checksum::default()
-    }
-
-    #[allow(dead_code, reason = "MinIO-parity surface with no caller in this port (backlog#1823)")]
-    fn new_checksum_string(t: ChecksumMode, s: &str) -> Result<Checksum, std::io::Error> {
-        let b = match base64_decode(s.as_bytes()) {
-            Ok(b) => b,
-            Err(err) => return Err(std::io::Error::other(err.to_string())),
-        };
-        if t.is_set() && b.len() == t.raw_byte_len() {
-            return Ok(Checksum {
-                checksum_type: t,
-                r: b,
-                computed: false,
-            });
-        }
-        Ok(Checksum::default())
-    }
-
     fn is_set(&self) -> bool {
         self.checksum_type.is_set() && self.r.len() == self.checksum_type.raw_byte_len()
     }
@@ -417,14 +375,17 @@ impl Checksum {
         }
         base64_encode(&self.r)
     }
+}
 
-    #[allow(dead_code, reason = "MinIO-parity surface with no caller in this port (backlog#1823)")]
-    fn raw(&self) -> Option<Vec<u8>> {
-        if !self.is_set() {
-            return None;
-        }
-        Some(self.r.clone())
-    }
+/// Read the base64 digest carried by `mode`'s `x-amz-checksum-*` response
+/// header, or an empty string when the header is absent (the client's
+/// datatypes use `""` for "no checksum").
+pub fn checksum_header_value(headers: &http::HeaderMap, mode: ChecksumMode) -> String {
+    headers
+        .get(mode.key())
+        .and_then(|value| value.to_str().ok())
+        .unwrap_or("")
+        .to_string()
 }
 
 pub fn add_auto_checksum_headers(opts: &mut PutObjectOptions) {
@@ -448,7 +409,7 @@ pub fn apply_auto_checksum(opts: &mut PutObjectOptions, all_parts: &mut [ObjectP
         let crc = opts.auto_checksum.full_object_checksum(all_parts)?;
         opts.user_metadata = {
             let mut hm = HashMap::new();
-            hm.insert(opts.auto_checksum.key_capitalized(), crc.encoded());
+            hm.insert(opts.auto_checksum.key(), crc.encoded());
             hm.insert("X-Amz-Checksum-Type".to_string(), "FULL_OBJECT".to_string());
             hm
         }
diff --git a/crates/s3-client/src/transition_api.rs b/crates/s3-client/src/transition_api.rs
index 87614ee84..6f45c76e2 100644
--- a/crates/s3-client/src/transition_api.rs
+++ b/crates/s3-client/src/transition_api.rs
@@ -19,7 +19,6 @@
 #![allow(clippy::all)]
 
 use crate::bucket_cache::BucketLocationCache;
-use crate::checksum::ChecksumMode;
 use crate::{
     api_error_response::ErrorResponse,
     api_error_response::{err_invalid_argument, http_resp_to_error_response, to_error_response},
@@ -898,7 +897,6 @@ pub struct RequestMetadata {
     pub content_md5_base64: String,
     pub content_sha256_hex: String,
     pub stream_sha256: bool,
-    pub add_crc: ChecksumMode,
     pub trailer: HeaderMap,
 }
 
diff --git a/scripts/ecstore-module-lint-register.txt b/scripts/ecstore-module-lint-register.txt
index ccb10b437..bf777b0f7 100644
--- a/scripts/ecstore-module-lint-register.txt
+++ b/scripts/ecstore-module-lint-register.txt
@@ -59,9 +59,6 @@ crates/s3-client/src/api_stat.rs|unused_variables
 crates/s3-client/src/bucket_cache.rs|clippy::all
 crates/s3-client/src/bucket_cache.rs|unused_must_use
 crates/s3-client/src/bucket_cache.rs|unused_variables
-crates/s3-client/src/checksum.rs|clippy::all
-crates/s3-client/src/checksum.rs|unused_must_use
-crates/s3-client/src/checksum.rs|unused_variables
 crates/s3-client/src/constants.rs|unused_must_use
 crates/s3-client/src/constants.rs|unused_variables
 crates/s3-client/src/credentials.rs|clippy::all