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Check whether a private key matches a certificate

harmless rootSSL and certificatesalle
Adjust the values, the command updates live
root@server
openssl x509 -noout -modulus -in /etc/ssl/certs/example.com.crt | openssl md5 && openssl rsa -noout -modulus -in /etc/ssl/private/example.com.key | openssl md5

Prints two MD5 checksums, one for the modulus of the certificate and one for that of the private key. If both are identical, key and certificate belong together. If they differ, the web server will not start or reports key values mismatch.

Note: Only works with RSA keys. For ECDSA, compare the public keys instead: openssl x509 -noout -pubkey -in cert.pem against openssl pkey -pubout -in key.pem.

Also searched as

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  • which key belongs to this certificate

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Check the SSL certificate expiration date of a website

$openssl s_client -connect example.com:443 -servername example.com </dev/null 2>/dev/null | openssl x509 -noout -dates
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Check whether a certificate expires within the next days

#openssl x509 -in /etc/letsencrypt/live/example.com/cert.pem -noout -checkend $(( 30 * 86400 )) && echo "noch gültig" || echo "läuft bald ab"
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Check whether a website's certificate is trusted

$openssl s_client -connect example.com:443 -servername example.com -verify_hostname example.com </dev/null 2>/dev/null | grep "Verify return code"
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Create a self-signed certificate for testing

$openssl req -x509 -newkey rsa:2048 -nodes -days 365 -keyout test.key -out test.crt -subj "/CN=test.example.com" -addext "subjectAltName=DNS:test.example.com"
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Generate a private key and CSR for multiple domains

$openssl req -new -newkey rsa:2048 -nodes -keyout example.com.key -out example.com.csr -subj "/CN=example.com" -addext "subjectAltName=DNS:example.com,DNS:www.example.com"
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Read all domains of a certificate (SAN)

$openssl s_client -connect example.com:443 -servername example.com </dev/null 2>/dev/null | openssl x509 -noout -ext subjectAltName
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