diff --git a/challenge/bin/adlin b/challenge/bin/adlin
index 8ce238a..4658bd2 100755
--- a/challenge/bin/adlin
+++ b/challenge/bin/adlin
@@ -17,7 +17,7 @@ token_generator() {
 	do
 	    echo -n :${d}
 	done
-    } | b2sum | cut -d ' ' -f 1
+    } | sha512sum | cut -d ' ' -f 1
 }
 
 # JSON token format helper
diff --git a/challenge/init b/challenge/init
index ba1490c..4e64d87 100755
--- a/challenge/init
+++ b/challenge/init
@@ -61,7 +61,7 @@ N2=$((25 + $RANDOM % 50))
 {
     echo -n $N1
     echo -n $N2
-    echo ${USER_PKEY:$N1:$N2} | b2sum | cut -d " " -f 1
+    echo -n ${USER_PKEY:$N1:$N2} | sha512sum | cut -d " " -f 1
 
 } > /mnt/token4
 sync
diff --git a/token-validator/challenge.go b/token-validator/challenge.go
index 99a7255..52680c7 100644
--- a/token-validator/challenge.go
+++ b/token-validator/challenge.go
@@ -2,6 +2,7 @@ package main
 
 import (
 	"crypto/hmac"
+	"crypto/sha512"
 	"encoding/hex"
 	"encoding/json"
 	"errors"
@@ -13,7 +14,6 @@ import (
 	"time"
 
 	"github.com/julienschmidt/httprouter"
-	"golang.org/x/crypto/blake2b"
 )
 
 const IPgwDMZ = "172.23.200.1"
@@ -129,7 +129,7 @@ func challengeDisk(s *Student, t *givenToken, chid int) error {
 		return err
 	}
 
-	expectedToken := blake2b.Sum512([]byte(pkey[n1:n2]))
+	expectedToken := sha512.Sum512([]byte(pkey[n1:n2]))
 
 	if ! hmac.Equal(expectedToken[:], sum) {
 		return errors.New("This is not the expected token.")
diff --git a/token-validator/token.go b/token-validator/token.go
index d00320e..168d6e7 100644
--- a/token-validator/token.go
+++ b/token-validator/token.go
@@ -1,19 +1,14 @@
 package main
 
 import (
+	"crypto/sha512"
 	"fmt"
-
-	"golang.org/x/crypto/blake2b"
 )
 
 func GenerateToken(pkey []byte, id int, a... []byte) ([]byte, error) {
-	h, err := blake2b.New(blake2b.Size, nil)
-	if err != nil {
-		return nil, err
-	}
+	h := sha512.New()
 
-	h.Write(pkey)
-	h.Write([]byte(fmt.Sprintf(":%d", id)))
+	h.Write([]byte(fmt.Sprintf("%x:%d", pkey, id)))
 
 	for _, v := range a {
 		h.Write([]byte(":"))