diff --git a/src/main/java/me/hatter/tool/signpdf/sign/SigUtils.java b/src/main/java/me/hatter/tool/signpdf/sign/SigUtils.java
index 38fda2c..486893c 100644
--- a/src/main/java/me/hatter/tool/signpdf/sign/SigUtils.java
+++ b/src/main/java/me/hatter/tool/signpdf/sign/SigUtils.java
@@ -112,7 +112,7 @@ public class SigUtils {
         COSDictionary referenceDict = new COSDictionary();
         referenceDict.setItem(COSName.TYPE, COSName.getPDFName("SigRef"));
         referenceDict.setItem("TransformMethod", COSName.DOCMDP);
-        referenceDict.setItem("DigestMethod", COSName.getPDFName("SHA1"));
+        referenceDict.setItem("DigestMethod", COSName.getPDFName("SHA256"));
         referenceDict.setItem("TransformParams", transformParameters);
         referenceDict.setNeedToBeUpdated(true);