Revert "feat(enhancement): Use crypto/sha256 instead of crypto/md5 for FIPS compliance (#1056)"

This reverts commit da8d2ee.

Author: jeevatkm

util.go

@@ -7,8 +7,8 @@ package resty
 
 import (
 	"bytes"
+	"crypto/md5"
 	"crypto/rand"
-	"crypto/sha256"
 	"encoding/binary"
 	"encoding/hex"
 	"errors"
@@ -371,7 +371,7 @@ func newGUID() string {
 	// Timestamp, 4 bytes, big endian
 	binary.BigEndian.PutUint32(b[:], uint32(time.Now().Unix()))
 
-	// Machine, first 3 bytes of sha256.Sum256([]byte(hostname))
+	// Machine, first 3 bytes of md5(hostname)
 	b[4], b[5], b[6] = machineID[0], machineID[1], machineID[2]
 
 	// Pid, 2 bytes, specs don't specify endianness, but we use big endian.
@@ -403,12 +403,13 @@ var osHostname = os.Hostname
 // readMachineID generates and returns a machine id.
 // If this function fails to get the hostname it will cause a runtime error.
 func readMachineID() []byte {
-	const idSize = 3
-	id := make([]byte, idSize)
+	var sum [3]byte
+	id := sum[:]
 
 	if hostname, err := osHostname(); err == nil {
-		hash := sha256.Sum256([]byte(hostname))
-		copy(id, hash[:idSize])
+		hw := md5.New()
+		_, _ = hw.Write([]byte(hostname))
+		copy(id, hw.Sum(nil))
 		return id
 	}