diff --git a/google-cloud-storage/lib/google/cloud/storage/file/verifier.rb b/google-cloud-storage/lib/google/cloud/storage/file/verifier.rb
index 52bf667bf976..c6d3626f7a77 100644
--- a/google-cloud-storage/lib/google/cloud/storage/file/verifier.rb
+++ b/google-cloud-storage/lib/google/cloud/storage/file/verifier.rb
@@ -48,32 +48,55 @@ def self.verify_md5 gcloud_file, local_file
           def self.verify_crc32c gcloud_file, local_file
             gcloud_file.crc32c == crc32c_for(local_file)
           end
+          # Calculates MD5 digest using either file path or open stream.
+          def self.md5_for(local_file)
+            _digest_for(local_file, ::Digest::MD5)
+          end
 
-          def self.md5_for local_file
-            if local_file.respond_to? :to_path
-              ::File.open Pathname(local_file).to_path, "rb" do |f|
-                ::Digest::MD5.file(f).base64digest
-              end
-            else # StringIO
-              (local_file = ::File.open Pathname(local_file)) unless local_file.respond_to? :rewind
-              local_file.rewind
-              md5 = ::Digest::MD5.base64digest local_file.read
-              local_file.rewind
-              md5
-            end
+          # Calculates CRC32c digest using either file path or open stream.
+          def self.crc32c_for(local_file)
+            _digest_for(local_file, ::Digest::CRC32c)
           end
 
-          def self.crc32c_for local_file
-            if local_file.respond_to? :to_path
+          private
+
+          # @private
+          # Computes a base64-encoded digest for a local file or IO stream.
+          #
+          # This method handles two types of inputs for `local_file`:
+          # 1. A file path (String or Pathname): It efficiently streams the file
+          #    to compute the digest without loading the entire file into memory.
+          # 2. An IO-like stream (e.g., File, StringIO): It reads the stream's
+          #    content to compute the digest. The stream is rewound before and after
+          #    reading to ensure its position is not permanently changed.
+          #
+          # @param local_file [String, Pathname, IO] The local file path or IO
+          #   stream for which to compute the digest.
+          # @param digest_class [Class] The digest class to use for the
+          #   calculation (e.g., `Digest::MD5`). It must respond to `.file` and
+          #   `.base64digest`.
+          #
+          # @return [String] The base64-encoded digest of the file's content.
+          #
+          def self._digest_for(local_file, digest_class)
+            if local_file.respond_to?(:to_path)
+              # Case 1: Input is a file path (or Pathname). Use the safe block form.
               ::File.open Pathname(local_file).to_path, "rb" do |f|
-                ::Digest::CRC32c.file(f).base64digest
+                digest_class.file(f).base64digest
+              end
+            else
+              # Case 2: Input is an open stream (like File or StringIO).
+              file_to_close = nil
+              file_to_close = local_file = ::File.open(Pathname(local_file).to_path, "rb") unless local_file.respond_to?(:rewind)
+              begin
+                local_file.rewind
+                digest = digest_class.base64digest local_file.read
+                local_file.rewind
+                digest
+              ensure
+                # Only close the stream if we explicitly opened it 
+                file_to_close.close if file_to_close.respond_to?(:close) && !file_to_close.closed?
               end
-            else # StringIO
-              (local_file = ::File.open Pathname(local_file)) unless local_file.respond_to? :rewind
-              local_file.rewind
-              crc32c = ::Digest::CRC32c.base64digest local_file.read
-              local_file.rewind
-              crc32c
             end
           end
         end