diff --git a/letsencrypt.sh b/letsencrypt.sh
index bc8e206..51249f2 100755
--- a/letsencrypt.sh
+++ b/letsencrypt.sh
@@ -1,69 +1,76 @@
 #!/bin/bash
 
-set -e
+set -eu
+
+. ./config.sh
+
+umask 077 # paranoid umask, we're creating private keys
 
-source config.sh
 
 urlbase64() {
   base64 -w 0 | sed -r 's/=*$//g' | tr '+/' '-_'
 }
+hex2bin() {
+  perl -pe 's/([0-9a-f]{2})/chr hex $1/gie'
+}
 
 signed_request() {
-  payload64="$(echo -n "${2}" | urlbase64)"
+  payload64="$(printf '%s' "${2}" | urlbase64)"
 
-  nonce="$(curl -s -I ${CA}/directory | grep Replay-Nonce | awk -F ': ' '{print $2}' | tr -d '\n\r')"
+  # -sSf: stay silent but report errors and exit with != 0 if they occur
+  nonce="$(curl -sSf -I "${CA}"/directory | grep Replay-Nonce: | awk -F ': ' '{print $2}' | tr -d '\n\r')"
 
   header='{"alg": "RS256", "jwk": {"e": "'"${pubExponent64}"'", "kty": "RSA", "n": "'"${pubMod64}"'"}}'
 
   protected='{"alg": "RS256", "jwk": {"e": "'"${pubExponent64}"'", "kty": "RSA", "n": "'"${pubMod64}"'"}, "nonce": "'"${nonce}"'"}'
-  protected64="$(echo -n "${protected}" | urlbase64)"
+  protected64="$(printf '%s' "${protected}" | urlbase64)"
 
-  signed64="$(echo -n "${protected64}.${payload64}" | openssl dgst -sha256 -sign private_key.pem | urlbase64)"
+  signed64="$(printf '%s' "${protected64}.${payload64}" | openssl dgst -sha256 -sign private_key.pem | urlbase64)"
 
   data='{"header": '"${header}"', "protected": "'"${protected64}"'", "payload": "'"${payload64}"'", "signature": "'"${signed64}"'"}'
 
-  curl -s -d "${data}" "${1}"
+  curl -sSf -d "${data}" "${1}"
 }
 
 sign_domain() {
   domain="${1}"
-  altnames="${@}"
-  echo "Signing domain ${1} (${@})..."
+  altnames="${*}"
+  echo "Signing domain ${1} (${*})..."
   if [ ! -e "certs/${domain}" ]; then
     SAN=""
     for altname in $altnames; do
       SAN+="DNS:${altname}, "
     done
-    SAN="$(echo -n $SAN | sed 's/,\s*$//g')"
+    SAN="$(printf '%s' "${SAN}" | sed 's/,\s*$//g')"
 
     mkdir "certs/${domain}"
 
     echo "  + Generating private key..."
     openssl genrsa -out "certs/${domain}/privkey.pem" 4096 2> /dev/null > /dev/null
     echo "  + Generating signing request..."
-    openssl req -new -sha256 -key "certs/${domain}/privkey.pem" -out "certs/${domain}/cert.csr" -subj "/CN=${domain}/" -reqexts SAN -config <(cat /etc/ssl/openssl.cnf <(printf "[SAN]\nsubjectAltName=${SAN}")) > /dev/null
+    openssl req -new -sha256 -key "certs/${domain}/privkey.pem" -out "certs/${domain}/cert.csr" -subj "/CN=${domain}/" -reqexts SAN -config <(cat /etc/ssl/openssl.cnf <(printf "[SAN]\nsubjectAltName=%s" "${SAN}")) > /dev/null
   fi
 
   for altname in $altnames; do
     echo "  + Requesting challenge for ${altname}..."
     response="$(signed_request "${CA}/acme/new-authz" '{"resource": "new-authz", "identifier": {"type": "dns", "value": "'"${altname}"'"}}')"
 
-    challenge_token="$(echo $response | grep -Eo '"challenges":[^\[]*\[[^]]*]' | sed 's/{/\n{/g' | grep 'http-01' | grep -Eo '"token":\s*"[^"]*"' | cut -d'"' -f4 | sed 's/[^A-Za-z0-9_\-]/_/g')"
-    challenge_uri="$(echo $response | grep -Eo '"challenges":[^\[]*\[[^]]*]' | sed 's/{/\n{/g' | grep 'http-01' | grep -Eo '"uri":\s*"[^"]*"' | cut -d'"' -f4)"
+    challenge_token="$(printf '%s\n' "${response}" | grep -Eo '"challenges":[^\[]*\[[^]]*]' | sed 's/{/\n{/g' | grep 'http-01' | grep -Eo '"token":\s*"[^"]*"' | cut -d'"' -f4 | sed 's/[^A-Za-z0-9_\-]/_/g')"
+    challenge_uri="$(printf '%s\n' "${response}" | grep -Eo '"challenges":[^\[]*\[[^]]*]' | sed 's/{/\n{/g' | grep 'http-01' | grep -Eo '"uri":\s*"[^"]*"' | cut -d'"' -f4)"
 
-    if [ "${challenge_token}" = "" ] || [ "${challenge_uri}" = "" ]; then
-      echo "  + Error: Can't retrieve challenges (${reqsponse})"
+    if [ -z "${challenge_token}" ] || [ -z "${challenge_uri}" ]; then
+      echo "  + Error: Can't retrieve challenges (${response})"
       exit 1
     fi
 
     keyauth="${challenge_token}.${thumbprint}"
 
-    echo -n "${keyauth}" > "${WELLKNOWN}/${challenge_token}"
+    printf '%s' "${keyauth}" > "${WELLKNOWN}/${challenge_token}"
 
     echo "  + Responding to challenge for ${altname}..."
     result="$(signed_request "${challenge_uri}" '{"resource": "challenge", "keyAuthorization": "'"${keyauth}"'"}')"
 
-    status="$(echo "${result}" | grep -Eo '"status":\s*"[^"]*"' | cut -d'"' -f4)"
+    status="$(printf '%s\n' "${result}" | grep -Eo '"status":\s*"[^"]*"' | cut -d'"' -f4)"
 
     if [ ! "${status}" = "pending" ] && [ ! "${status}" = "valid" ]; then
       echo "  + Challenge is invalid! (${result})"
@@ -71,7 +78,7 @@ sign_domain() {
     fi
 
     while [ ! "${status}" = "valid" ]; do
-      status="$(curl -s "${challenge_uri}" | grep -Eo '"status":\s*"[^"]*"' | cut -d'"' -f4)"
+      status="$(curl -sSf "${challenge_uri}" | grep -Eo '"status":\s*"[^"]*"' | cut -d'"' -f4)"
     done
 
     echo "  + Challenge is valid!"
@@ -80,7 +87,7 @@ sign_domain() {
   echo "  + Requesting certificate..."
   csr64="$(openssl req -in "certs/${domain}/cert.csr" -outform DER | urlbase64)"
   crt64="$(signed_request "${CA}/acme/new-cert" '{"resource": "new-cert", "csr": "'"${csr64}"'"}' | base64 -w 64)"
-  echo -e "-----BEGIN CERTIFICATE-----\n${crt64}\n-----END CERTIFICATE-----\n" > "certs/${domain}/cert.pem"
+  printf -- '-----BEGIN CERTIFICATE-----\n%s\n-----END CERTIFICATE-----\n' "${crt64}" > "certs/${domain}/cert.pem"
   echo "  + Done!"
 }
 
@@ -91,16 +98,16 @@ if [ ! -e "private_key.pem" ]; then
   register="1"
 fi
 
-pubExponent64="$(printf "%06x" "$(openssl rsa -in private_key.pem -noout -text | grep publicExponent | head -1 | cut -d' ' -f2)" | perl -pe 's/([0-9a-f]{2})/chr hex $1/gie' | urlbase64)"
-pubMod64="$(echo -n "$(openssl rsa -in private_key.pem -noout -modulus | cut -d'=' -f2 | perl -pe 's/([0-9a-f]{2})/chr hex $1/gie')" | urlbase64)"
+pubExponent64="$(printf "%06x" "$(openssl rsa -in private_key.pem -noout -text | grep publicExponent | head -1 | cut -d' ' -f2)" | hex2bin | urlbase64)"
+pubMod64="$(printf '%s' "$(openssl rsa -in private_key.pem -noout -modulus | cut -d'=' -f2)" | hex2bin | urlbase64)"
 
-thumbprint="$(echo -n "$(echo -n '{"e":"'"${pubExponent64}"'","kty":"RSA","n":"'"${pubMod64}"'"}' | sha256sum | awk '{print $1}' | perl -pe 's/([0-9a-f]{2})/chr hex $1/gie')" | urlbase64)"
+thumbprint="$(printf '%s' "$(printf '%s' '{"e":"'"${pubExponent64}"'","kty":"RSA","n":"'"${pubMod64}"'"}' | sha256sum | awk '{print $1}')" | hex2bin | urlbase64)"
 
 if [ "${register}" = "1" ]; then
   echo "+ Registering account key with letsencrypt..."
   signed_request "${CA}/acme/new-reg" '{"resource": "new-reg", "agreement": "https://letsencrypt.org/documents/LE-SA-v1.0.1-July-27-2015.pdf"}' > /dev/null
 fi
 
-cat domains.txt | sed 's/^\s*//g;s/\s*$//g' | grep -v '^#' | grep -v '^$' | while read line; do
-  sign_domain $line
+<domains.txt sed 's/^\s*//g;s/\s*$//g' | grep -v '^#' | grep -v '^$' | while read line; do
+  sign_domain "$line"
 done