HTTPS Certificates

New in version 1.3.

By default, pip will perform SSL certificate verification for network connections it makes over HTTPS. These serve to prevent man-in-the-middle attacks against package downloads. This does not use the system certificate store but, instead, uses a bundled CA certificate store from certifi.

Using a specific certificate store

The --cert option (and the corresponding PIP_CERT environment variable) allow users to specify a different certificate store/bundle for pip to use. It is also possible to use REQUESTS_CA_BUNDLE or CURL_CA_BUNDLE environment variables.

Using system certificate stores

New in version 22.2: Experimental support, behind --use-feature=truststore.

It is possible to use the system trust store, instead of the bundled certifi certificates for verifying HTTPS certificates. This approach will typically support corporate proxy certificates without additional configuration.

In order to use system trust stores, you need to use Python 3.10 or newer.

Linux

$ python -m pip install SomePackage --use-feature=truststore
[...]
Successfully installed SomePackage

MacOS

$ python -m pip install SomePackage --use-feature=truststore
[...]
Successfully installed SomePackage

Windows

C:> py -m pip install SomePackage --use-feature=truststore
[...]
Successfully installed SomePackage

When to use

You should try using system trust stores when there is a custom certificate chain configured for your system that pip isn’t aware of. Typically, this situation will manifest with an SSLCertVerificationError with the message “certificate verify failed: unable to get local issuer certificate”:

Linux

$ python -m pip install -U SomePackage
[...]
   SSLError(SSLCertVerificationError(1, '[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: unable to get local issuer certificate (\_ssl.c:997)'))) - skipping

MacOS

$ python -m pip install -U SomePackage
[...]
   SSLError(SSLCertVerificationError(1, '[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: unable to get local issuer certificate (\_ssl.c:997)'))) - skipping

Windows

C:> py -m pip install -U SomePackage
[...]
   SSLError(SSLCertVerificationError(1, '[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: unable to get local issuer certificate (\_ssl.c:997)'))) - skipping

This error means that OpenSSL wasn’t able to find a trust anchor to verify the chain against. Using system trust stores instead of certifi will likely solve this issue.

If you encounter a TLS/SSL error when using the truststore feature you should open an issue on the truststore GitHub issue tracker instead of pip’s issue tracker. The maintainers of truststore will help diagnose and fix the issue.