Skip to main content

SSL 常用技巧

Check TLS/SSL certificate expiration date

from a website)

# NOTE: openssl requires at least 1.1.1
SITE_URL="www.cloudcoin.global" 
SITE_SSL_PORT="443" 
## note echo added ## 
echo | openssl s_client -servername ${SITE_URL} -connect ${SITE_URL}:${SITE_SSL_PORT} \
| openssl x509 -noout -dates
# Alternaively
openssl s_client -connect ${SITE_URL}:${SITE_SSL_PORT} -servername ${SITE_URL} 2> /dev/null | openssl x509 -noout -dates

output

depth=2 C = IE, O = Baltimore, OU = CyberTrust, CN = Baltimore CyberTrust Root
verify return:1
depth=1 C = US, O = "Cloudflare, Inc.", CN = Cloudflare Inc ECC CA-3
verify return:1
depth=0 C = US, ST = CA, L = San Francisco, O = "Cloudflare, Inc.", CN = cloudcoin.global
verify return:1
DONE
notBefore=Jun  5 00:00:00 2020 GMT
notAfter=Jun  5 12:00:00 2021 GMT
  • s_client : The s_client command implements a generic SSL/TLS client which connects to a remote host using SSL/TLS.
  • -servername $DOM : Set the TLS SNI (Server Name Indication) extension in the ClientHello message to the given value. NOTE: openssl requires at lease 1.1.1
  • -connect $DOM:$PORT : This specifies the host ($DOM) and optional port ($PORT) to connect to.
  • x509 : Run certificate display and signing utility.
  • -noout : Prevents output of the encoded version of the certificate.
  • -dates : Prints out the start and expiry dates of a TLS or SSL certificate.

from a PEM encoded certificate file)

openssl x509 -enddate -noout -in /etc/nginx/ssl/www.cyberciti.biz.fullchain.cer

# find out if the TLS/SSL certificate expires within next 7 days (604800 seconds):
openssl x509 -enddate -noout -in my.pem -checkend 604800

output

notAfter=Dec 29 23:48:42 2020 GMT

Shell script to alert sysadmin

#!/bin/bash
# Purpose: Alert sysadmin/developer about the TLS/SSL cert expiry date in advance
# Author: Vivek Gite {https://www.cyberciti.biz/} under GPL v2.x+
# -------------------------------------------------------------------------------
PEM="/etc/nginx/ssl/letsencrypt/cyberciti.biz/cyberciti.biz.fullchain.cer"
 
# 7 days in seconds 
DAYS="604800" 
 
# Email settings 
_sub="$PEM will expire within $DAYS (7 days)."
_from="system-account@your-dommain"
_to="sysadmin@your-domain"
_openssl="/usr/bin/openssl"
$_openssl x509 -enddate -noout -in "$PEM"  -checkend "$DAYS" | grep -q 'Certificate will expire'
 
# Send email and push message to my mobile
if [ $? -eq 0 ]
then
	echo "${_sub}"
        mail -s "$_sub" -r "$_from" "$_to" <<< "Warning: The TLS/SSL certificate ($PEM) will expire soon on $HOSTNAME [$(date)]"
        # See https://www.cyberciti.biz/mobile-devices/android/how-to-push-send-message-to-ios-and-android-from-linux-cli/ #
        source ~/bin/cli_app.sh
        push_to_mobile "$0" "$_sub. See $_to email for detailed log. -- $HOSTNAME " >/dev/null
fi

With Python

Get the Server certificate from the website

NOTE: openssl requires at least 1.1.1

echo -n | openssl s_client -showcerts -servername some.web.site -connect some.web.site:443 | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' > some-web-site.pem

除了使用 openssl 以外，也可以用 Firefox 或 Chrome 手動下載 Server 憑證檔。

顯示憑證檔 *.crt, *.pem 的詳細資訊

憑證檔的內容是由兩字串 -----BEGIN CERTIFICATE----- 與 -----END CERTIFICATE----- 所包含的亂數組合，要解析其中的憑證資訊，可以使用 openssl 工具：

openssl x509 -text -noout -in my_CA.pem 
Check the TLS version
nmap --script ssl-enum-ciphers -p 443 www.google.com

# -tls1 for TLSv1
# -tls1_1 for TLSv1.1
# -tls1_2 for TLSv1.2
openssl s_client -connect www.google.com:443 -tls1_3
Generate a CSR (Certificate Signing Request)
sudo apt install openssl  #[On Debian/Ubuntu]
sudo yum install openssl  #[On CentOS/RHEL]
sudo dnf install openssl  #[On Fedora]

openssl req -new -newkey rsa:2048 -nodes -keyout example.com.key -out example.com.csr
Show the Information of the certificate
openssl x509 -noout -text -in your.cer

# For the cert file that is generated by Windows
openssl x509 -noout -text -inform der -in win.cer
More commands
# Generating a Private Key
openssl genpkey -algorithm RSA -out private.key 

# Generating a Certificate Signing Request (CSR) 
openssl req -new -key private.key -out csr.csr

# Generating a Self-Signed Certificate
openssl req -new -x509 -key private.key -out certificate.crt -days 365

# Encrypting Files
openssl enc -aes256 -in sensitive.txt -out sensitive.enc

# Decrypting Files 
openssl enc -aes256 -d -in sensitive.enc -out sensitive.txt

# Converting Certificate Formats
openssl x509 -in certificate.crt -out certificate.pem

# Creating a Certificate Chain
cat intermediate.crt root.crt > chain.crt

# Signing a CSR with a CA
openssl x509 -req -in csr.csr -CA ca.crt -CAkey ca.key -CAcreateserial -out certificate.crt -days 365

# Generating a Random Number
openssl rand -hex 16

# Checking CSR Details
openssl req -in csr.csr -noout -text

# Viewing Certificate Expiry
openssl x509 -enddate -noout -in certificate.crt

# Converting PFX to PEM
openssl pkcs12 -in certificate.pfx -clcerts -nokeys -out certificate.pem

# Creating a Password-Protected Private Key
openssl genpkey -algorithm RSA -aes256 -out private.key

# Testing SSLv2/v3 Protocol Support
openssl s_client -connect example[dot]com:443 -ssl2/-ssl3

# Extracting Public Key from Private Key
openssl rsa -in private.key -pubout -out public.key

# Encrypting and Decrypting Files with a Passphrase
# Encrypting File:
openssl enc -aes256 -salt -in sensitive.txt -out sensitive.enc
# Decrypting File:
openssl enc -aes256 -d -in sensitive.enc -out sensitive_decrypted.txt


No Comments
Back to top