Janik Vonrotz

2 min read

Find certificate files that will expire soon and create a csr

The certificate expiration period should be kept as short as possible in a public key infrastructure. But the cost of resigning certificates must not be too high. This trade off causes a lot of problems. Every now and then a certificate expires without anybody noticing it or the same certificate is used for 10 years, which is obviously a security risk. In order to avoid this problem you either use Let’s Encrypt or another fully automated certificate management system. If this is not available you must know at least which certificates are going to expire soon.

In my case I had a project with multiple certificate and dynamically built key stores. I had to find the certificates in the project folder structure that expire soon and need to be resigned. In order to automate this process I’ve built the following bash script.

# look for certificates that will expire before this date

# create numeric date from max age
intmaxage=$(date -d $maxage +%s)

# search for all pem files in current folder
for certfile in $(find ./ -name *.pem); do

    # filter files by certificates
    if [[ "$certfile" == *certificate.pem ]]

        # extract the not after date string
        noafter=$(openssl x509 -in $certfile -text -noout | grep 'Not After :' | cut -d':' -f2- | sed 's/ //')

        # convert it to a date value
        date=$(date --date="$noafter" "+%b %d %H:%M:%S %Y GMT")

        # convert date value to a numeric date
        intdate=$(date --date="$date" +%s)

        # set the key file
        keyfile=$(echo $certfile | sed 's/certificate.pem/key.pem/')

        # create csr file variable
        csrfile=$(basename $certfile | sed 's/certificate.pem/.csr/')

        # create new csr
        openssl req -out ~/$csrfile -key $keyfile -new

        # check if certificate expires before the max age
        if [[ $intdate -le $intmaxage ]]

            # confirm the creation of the csr and provide meta information
            echo "A csr file: $csrfile"
            echo "for the certificate: $certfile"
            echo "with key file: $keyfile"
            echo "has been create as it will expire soon at: $date"
            echo ""

Categories: Scripting
Tags: bash , openssl
Improve this page
Show statistic for this page