diff a/src/java.base/share/classes/sun/security/tools/keytool/Main.java b/src/java.base/share/classes/sun/security/tools/keytool/Main.java
--- a/src/java.base/share/classes/sun/security/tools/keytool/Main.java
+++ b/src/java.base/share/classes/sun/security/tools/keytool/Main.java
@@ -1466,11 +1466,11 @@
                     new CertificateAlgorithmId(algID));
         info.set(X509CertInfo.ISSUER, issuer);
 
         BufferedReader reader = new BufferedReader(new InputStreamReader(in));
         boolean canRead = false;
-        StringBuffer sb = new StringBuffer();
+        StringBuilder sb = new StringBuilder();
         while (true) {
             String s = reader.readLine();
             if (s == null) break;
             // OpenSSL does not use NEW
             //if (s.startsWith("-----BEGIN NEW CERTIFICATE REQUEST-----")) {
@@ -2623,11 +2623,11 @@
 
     private void doPrintCertReq(InputStream in, PrintStream out)
             throws Exception {
 
         BufferedReader reader = new BufferedReader(new InputStreamReader(in));
-        StringBuffer sb = new StringBuffer();
+        StringBuilder sb = new StringBuilder();
         boolean started = false;
         while (true) {
             String s = reader.readLine();
             if (s == null) break;
             if (!started) {
@@ -3543,37 +3543,10 @@
             out.write(cert.getEncoded()); // binary
         }
     }
 
     /**
-     * Converts a byte to hex digit and writes to the supplied buffer
-     */
-    private void byte2hex(byte b, StringBuffer buf) {
-        char[] hexChars = { '0', '1', '2', '3', '4', '5', '6', '7', '8',
-                            '9', 'A', 'B', 'C', 'D', 'E', 'F' };
-        int high = ((b & 0xf0) >> 4);
-        int low = (b & 0x0f);
-        buf.append(hexChars[high]);
-        buf.append(hexChars[low]);
-    }
-
-    /**
-     * Converts a byte array to hex string
-     */
-    private String toHexString(byte[] block) {
-        StringBuffer buf = new StringBuffer();
-        int len = block.length;
-        for (int i = 0; i < len; i++) {
-             byte2hex(block[i], buf);
-             if (i < len-1) {
-                 buf.append(":");
-             }
-        }
-        return buf.toString();
-    }
-
-    /**
      * Recovers (private) key associated with given alias.
      *
      * @return an array of objects, where the 1st element in the array is the
      * recovered private key, and the 2nd element is the password used to
      * recover it.
@@ -3698,11 +3671,11 @@
         throws Exception
     {
         byte[] encCertInfo = cert.getEncoded();
         MessageDigest md = MessageDigest.getInstance(mdAlg);
         byte[] digest = md.digest(encCertInfo);
-        return toHexString(digest);
+        return Hex.encoder(":","", "", true).encode(digest);
     }
 
     /**
      * Prints warning about missing integrity check.
      */
@@ -4610,19 +4583,14 @@
                         ObjectIdentifier oid = ObjectIdentifier.of(name);
                         byte[] data = null;
                         if (value != null) {
                             data = new byte[value.length() / 2 + 1];
                             int pos = 0;
+                            Hex.Decoder decoder = Hex.decoder();
                             for (char c: value.toCharArray()) {
-                                int hex;
-                                if (c >= '0' && c <= '9') {
-                                    hex = c - '0' ;
-                                } else if (c >= 'A' && c <= 'F') {
-                                    hex = c - 'A' + 10;
-                                } else if (c >= 'a' && c <= 'f') {
-                                    hex = c - 'a' + 10;
-                                } else {
+                                int hex = decoder.fromHex(c);
+                                if (hex < 0) {
                                     continue;
                                 }
                                 if (pos % 2 == 0) {
                                     data[pos/2] = (byte)(hex << 4);
                                 } else {