diff --git a/samples/certs/all.sh b/samples/certs/all.sh
index 8c842dc..7e1aa98 100755
--- a/samples/certs/all.sh
+++ b/samples/certs/all.sh
@@ -1,4 +1,4 @@
-#!/usr/bin/env sh
+#!/bin/sh
 ./rootA.sh
 ./rootB.sh
 ./clientA.sh
diff --git a/samples/certs/clientA.sh b/samples/certs/clientA.sh
index 0f0657d..118e186 100755
--- a/samples/certs/clientA.sh
+++ b/samples/certs/clientA.sh
@@ -1,4 +1,4 @@
-#!/usr/bin/env sh
+#!/bin/sh
 
 openssl req -newkey rsa:2048 -sha256 -keyout clientAkey.pem -out clientAreq.pem \
   -nodes -config ./clientA.cnf -days 365 -batch
diff --git a/samples/certs/clientB.sh b/samples/certs/clientB.sh
index 8718468..a39ae83 100755
--- a/samples/certs/clientB.sh
+++ b/samples/certs/clientB.sh
@@ -1,4 +1,4 @@
-#!/usr/bin/env sh
+#!/bin/sh
 
 openssl req -newkey rsa:2048 -sha256 -keyout clientBkey.pem -out clientBreq.pem \
   -nodes -config ./clientB.cnf -days 365 -batch
diff --git a/samples/certs/rootA.sh b/samples/certs/rootA.sh
index 6d29126..fcfcd73 100755
--- a/samples/certs/rootA.sh
+++ b/samples/certs/rootA.sh
@@ -1,4 +1,4 @@
-#!/usr/bin/env sh
+#!/bin/sh
 
 openssl req -newkey rsa:2048 -sha256 -keyout rootAkey.pem -out rootAreq.pem -nodes -config ./rootA.cnf -days 365 -batch
 
diff --git a/samples/certs/rootB.sh b/samples/certs/rootB.sh
index fabc3a5..07b53a4 100755
--- a/samples/certs/rootB.sh
+++ b/samples/certs/rootB.sh
@@ -1,4 +1,4 @@
-#!/usr/bin/env sh
+#!/bin/sh
 
 openssl req -newkey rsa:2048 -sha256 -keyout rootBkey.pem -out rootBreq.pem -nodes -config ./rootB.cnf -days 365 -batch
 
diff --git a/samples/certs/serverA.sh b/samples/certs/serverA.sh
index 66e8441..9fcf5dc 100755
--- a/samples/certs/serverA.sh
+++ b/samples/certs/serverA.sh
@@ -1,6 +1,6 @@
-#!/usr/bin/env sh
+#!/bin/sh
 
-openssl req -newkey rsa:2048 -keyout serverAkey.pem -out serverAreq.pem \
+openssl req -newkey rsa:2048 -sha256 -keyout serverAkey.pem -out serverAreq.pem \
    -config ./serverA.cnf -nodes -days 365 -batch
 
 openssl x509 -req -in serverAreq.pem -sha256 -extfile ./serverA.cnf \
diff --git a/samples/certs/serverB.sh b/samples/certs/serverB.sh
index ee127ea..f184b1c 100755
--- a/samples/certs/serverB.sh
+++ b/samples/certs/serverB.sh
@@ -1,6 +1,6 @@
-#!/usr/bin/env sh
+#!/bin/sh
 
-openssl req -newkey rsa:2048 -keyout serverBkey.pem -out serverBreq.pem \
+openssl req -newkey rsa:2048 -sha256 -keyout serverBkey.pem -out serverBreq.pem \
    -config ./serverB.cnf -nodes -days 365 -batch
 
 openssl x509 -req -in serverBreq.pem -sha256 -extfile ./serverB.cnf \