OpenSSL Notes

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OpenSSL tasks

Creating a CSR and/or self-signed certificate

create the private key and certificate signing request

cn='www.example.com'
openssl req -newkey rsa:4096 > ${cn}.csr
  • Step two - remove the passphrase from the key (optional):
 openssl rsa -in privkey.pem -out ${cn}.key
  • Step three (optional) - convert the CSR into a self-signed certificate:
  openssl x509 -in ${cn}.csr -out ${cn}.crt -req -signkey ${cn}.key -days 365

This will produce a self-signed cert that can be used for any SSL service.

For example, the Apache-SSL directives are as follows:

 SSLCertificateFile /path/to/certs/new.cert.cert
 SSLCertificateKeyFile /path/to/certs/new.cert.key

create CSR with SANs

export sans="[SAN]\nsubjectAltName=DNS:example.com,DNS:www.example.com,DNS:www2.example.com\n"
cp /etc/pki/tls/openssl.cnf /root/ssl/
printf $sans >> /root/ssl/openssl.cnf
openssl req -new -sha256 -key site.example.key -reqexts SAN -config /root/ssl/openssl.cnf -subj '/C=US/ST=Michigan/L=Mason/O=Example Corp/OU=IT/CN=server.example.com/emailAddress=it@example.com'

Generate a password hash (md5)

echo "blah" | openssl passwd -1 -stdin

Verify a server certificate

You can test an SSL connection using the s_client option.

openssl s_client -connect <server>:<port>

For servers using TLS you can use the -starttls command.

openssl s_client -showcerts -starttls smtp -connect host.example.com:25
openssl s_client -showcerts -connect  www.example.com:443 -tls1_2

Testing with a client cert:

openssl s_client -key <keyfile> -cert <cert> -CAfile <cafile> -connect <server>:8081

Extract cert used for a connection

openssl s_client -connect www.example.com:443 -tls1_2 2>&1 | sed --quiet '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' > www.example.com.crt

Check cert details

openssl x509 -in certificate.crt -text -noout

Verifying that a key and certificate match

To verify that a certificate and key file match you can compare certificate modulus on each cert to look for a match. The `modulus' and the `public exponent' portions of the key and the certificate must match. The following commands will produce an md5 sum which can be used to find the key that matches a cert or vice versa.

openssl x509 -noout -modulus -in server.crt | openssl md5
openssl rsa -noout -modulus -in server.key | openssl md5

Converting SSL certs

Convert PFX to PEM:

openssl pkcs12 -in c:\certs\yourcert.pfx -out c:\certs\cag.pem -nodes

Convert cert file to PFX:

#!/bin/bash
[ -n "$1" -a "$2" ]  || { echo "Usage: ./crt2pfx cert.crt .keyfile cert_name"; exit 0 ; }

openssl x509 -in $1 -out input.der -outform DER;

openssl x509 -in input.der -inform DER -out output.pem -outform PEM;

openssl pkcs12 -export -in output.pem -inkey $2 -out $3.pfx -name "$3";

echo "cleaning up...";
sleep 1;

echo "Removing input.der";
rm input.der;
sleep 1;

echo "Removing output.pem";
rm output.pem;
sleep 1;

exit 0;

List installed CA certs

awk -v cmd='openssl x509 -noout -subject' '/BEGIN/{close(cmd)};{print | cmd}' < /etc/pki/tls/cert.pem

If you're checking for a specific cert you can grep for the common name.

awk -v cmd='openssl x509 -noout -subject' '/BEGIN/{close(cmd)};{print | cmd}' < /etc/pki/tls/cert.pem  | grep -E "Dart|DCIssuing"

Fix ASN errors

If you see errors similar to below you will need to convert the certificate file into the proper encoding.

Openssl Unable to Load Certificate Wrong Asn1 Encoding routines:ASN 1_CHECK_TLEN::tag:tasn_dec.c:1319

140735207381436:error:0D0680A8:asn1 encoding routines:ASN1_CHECK_TLEN:wrong tag:tasn_dec.c:1319:
140735207381436:error:0D07803A:asn1 encoding routines:ASN1_ITEM_EX_D2I:nested asn1 error:tasn_dec.c:381:Type=X509_CINF
140735207381436:error:0D08303A:asn1 encoding routines:ASN1_TEMPLATE_NOEXP_D2I:nested asn1 error:tasn_dec.c:751:Field=cert_info, Type=X509
140735207381436:error:0906700D:PEM routines:PEM_ASN1_read_bio:ASN1 lib:pem_oth.c:83:

While the certificate file visually appears to be in x.509 format, you will find it contains a far longer base64 string than x.509 certificates of the same bit length. The format in this case is p7b (PCKS #7). To convert the cert to x509 format run this command.

openssl pkcs7 -print_certs -in certificate.p7b -out certificate.cer

References

https://www.feistyduck.com/library/openssl-cookbook/online/ch-testing-with-openssl.html

http://www.madboa.com/geek/openssl/#cert-test

https://langui.sh/2009/03/14/checking-a-remote-certificate-chain-with-openssl/

http://blog.oneiroi.co.uk/openssl/x.509/pcks7/openssl-unable-to-load-certificate-wrong-asn1-encoding-routines-asn1-check-tlen-tag-tasn-dec-dot-c-1319/