I recently encountered the error message ERR_SSL_KEY_USAGE_INCOMPATIBLE in chrome using a self signed certificate. I spent hours trying to solve the problem before finally re-generating the certificate with:

openssl req -new -x509 -days 36500 -nodes -newkey rsa:2048 -keyout cert.key -out cert.crt -extensions v3_req

Hope this helps someone else.

  • Actually - you want to post the solution as an answer (Its perfectly fine). Might also help to say where you're using this cert, just for completeness sake. – Journeyman Geek Jun 23 at 9:08
  • This helped me with a broken CUPS ssl cert with RHEL 8. – NoelProf Jul 12 at 21:21

I solve this problem by changing keyUsage = keyEncipherment, dataEncipherment to keyUsage = nonRepudiation, digitalSignature, keyEncipherment in the section v3_req in file req.conf like acme.sh does, There's no error with chrome 75 now.

My problem might be a little different. It is ok with original configuration with tls1.2, but ERR_SSL_KEY_USAGE_INCOMPATIBLE with tls1.3.

The command to generate certification is as following.

openssl req -x509 -nodes -days 3650 -newkey rsa:4096 -keyout cert.key -out cert.cer -config req.conf -extensions v3_req

full content of my req.conf

distinguished_name = req_distinguished_name
x509_extensions = v3_req
prompt = no
C = US
ST = California
L = Los Angeles
O = Internet Corporation for Assigned Names and Numbers
OU = IT Operations
CN = home.arpa
keyUsage = nonRepudiation, digitalSignature, keyEncipherment
extendedKeyUsage = serverAuth
subjectAltName = @alt_names
DNS.1 = home.arpa
DNS.2 = *.home.arpa
IP.1 =

This issue is related to the value of the 'KeyUsage' parameter in the SSL config of 'v3_req'.

Removing 'KeyUsage' from the config will imply that any usage is valid for the certificate. For some reason (which I haven't yet determined) if keyusage is specified Chrome 75/76 will reject the Key for self-signed certificates over localhost.

Removing the 'KeyUsage' paramater from v3_req and regenerating the certifcate fixes the issue, hence the command posted by Tiffany will work as no KeyUsage is specified.

protected by Ramhound Aug 1 at 3:31

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