How do I edit a self signed certificate created using openssl xampp?

Question

I created my own self signed certificate using openssl which is built in in xampp. However, I want to edit the common name, is this possible? Does anyone know how I can overwrite the certificate?

Solution

However, I want to edit the common name, is this possible? Does anyone know how I can overwrite the certificate?

Its not possible per se. The Common Name (CN) is in the part of the certificate that is signed, so you can't simply remove it without invalidating the signature.

However, you can simply generate a new certificate request or self-signed certificate with DNS names in the Subject Alternate Name (SAN) (and not in the Common Name (CN)).

The trick to creating a self signed certificate with DNS names in the SAN is you need to use a custom configuration file. You can't generate one using just the command line because the DNS names in the SAN are not copied. Below is the custom CONF file I use (called example-com.conf).

---

example-com.conf:

# Self Signed (note the addition of -x509):
#     openssl req -config example-com.conf -new -x509 -sha256 -newkey rsa:2048 -nodes -keyout example-com.key.pem -days 365 -out example-com.cert.pem
# Signing Request (note the lack of -x509):
#     openssl req -config example-com.conf -new -newkey rsa:2048 -nodes -keyout example-com.key.pem -days 365 -out example-com.req.pem
# Print it:
#     openssl x509 -in example-com.cert.pem -text -noout
#     openssl req -in example-com.req.pem -text -noout

[ req ]
default_bits        = 2048
default_keyfile     = server-key.pem
distinguished_name  = subject
req_extensions      = req_ext
x509_extensions     = x509_ext
string_mask         = utf8only

# The Subject DN can be formed using X501 or RFC 4514 (see RFC 4519 for a description).
#   Its sort of a mashup. For example, RFC 4514 does not provide emailAddress.
[ subject ]
countryName         = Country Name (2 letter code)
countryName_default     = US

stateOrProvinceName     = State or Province Name (full name)
stateOrProvinceName_default = NY

localityName            = Locality Name (eg, city)
localityName_default        = New York

organizationName         = Organization Name (eg, company)
organizationName_default    = Example, LLC

# Use a friendly name here because its presented to the user. The server's DNS
#   names are placed in Subject Alternate Names. Plus, DNS names here is deprecated
#   by both IETF and CA/Browser Forums. If you place a DNS name here, then you 
#   must include the DNS name in the SAN too (otherwise, Chrome and others that
#   strictly follow the CA/Browser Baseline Requirements will fail).
commonName          = Common Name (e.g. server FQDN or YOUR name)
commonName_default      = Example Company

emailAddress            = Email Address
emailAddress_default        = [email protected]

# Section x509_ext is used when generating a self-signed certificate. I.e., openssl req -x509 ...
[ x509_ext ]

subjectKeyIdentifier        = hash
authorityKeyIdentifier  = keyid,issuer

basicConstraints        = CA:FALSE
keyUsage            = digitalSignature, keyEncipherment
subjectAltName          = @alternate_names
nsComment           = "OpenSSL Generated Certificate"

# RFC 5280, Section 4.2.1.12 makes EKU optional
# CA/Browser Baseline Requirements, Appendix (B)(3)(G) makes me confused
# extendedKeyUsage  = serverAuth, clientAuth

# Section req_ext is used when generating a certificate signing request. I.e., openssl req ...
[ req_ext ]

subjectKeyIdentifier        = hash

basicConstraints        = CA:FALSE
keyUsage            = digitalSignature, keyEncipherment
subjectAltName          = @alternate_names
nsComment           = "OpenSSL Generated Certificate"

# RFC 5280, Section 4.2.1.12 makes EKU optional
# CA/Browser Baseline Requirements, Appendix (B)(3)(G) makes me confused
# extendedKeyUsage  = serverAuth, clientAuth

[ alternate_names ]

DNS.1       = example.com
DNS.2       = www.example.com
DNS.3       = mail.example.com
DNS.4       = ftp.example.com

# Add these if you need them. But usually you don't want them or
#   need them in production. You may need them for development.
# DNS.5       = localhost
# DNS.6       = localhost.localdomain
# DNS.7       = 127.0.0.1

# IPv6 localhost
# DNS.8     = ::1