fune/browser/extensions/disableSHA1rollout

This system add-on is a follow-up to the MITM prevalence experiment. The purpose is to facilitate rolling out the disabling of SHA-1 in signatures on certificates issued by publicly-trusted roots. When installed, this add-on will perform a number of checks to determine if it should change the preference that controls the SHA-1 policy. First, this should only apply to users on the beta update channel. It should also only apply to users who have not otherwise changed the policy to always allow or always forbid SHA-1. Additionally, it must double-check that the user is not affected by a TLS intercepting proxy using a publicly-trusted root. If these checks pass, the add-on will divide the population into a test group and a control group (starting on a 10%/90% split). The test group will have the policy changed. After doing this, a telemetry payload is reported with the following values:

• cohortName -- the name of the group this user is in:
  1. "notSafeToDisableSHA1" if the user is behind a MITM proxy using a publicly-trusted root
  2. "optedOut" if the user already set the SHA-1 policy to always allow or always forbid
  3. "optedIn" if the user already set the SHA-1 policy to only allow for non-built-in roots
  4. "test" if the user is in the test cohort (and SHA-1 will be disabled)
  5. "control" if the user is not in the test cohort
• errorCode -- 0 for successful connections, some PR error code otherwise
• error -- a short description of one of four error conditions encountered, if applicable, and an empty string otherwise:
  1. "timeout" if the connection to telemetry.mozilla.org timed out
  2. "user override" if the user has stored a permanent certificate exception override for telemetry.mozilla.org (due to technical limitations, we can't gather much information in this situation)
  3. "certificate reverification" if re-building the certificate chain after connecting failed for some reason (unfortunately this step is necessary due to technical limitations)
  4. "connection error" if the connection to telemetry.mozilla.org failed for another reason
• chain -- a list of dictionaries each corresponding to a certificate in the verified certificate chain, if it was successfully constructed. The first entry is the end-entity certificate. The last entry is the root certificate. This will be empty if the connection failed or if reverification failed. Each element in the list contains the following values:
  • sha256Fingerprint -- a hex string representing the SHA-256 hash of the certificate
  • isBuiltInRoot -- true if the certificate is a trust anchor in the web PKI, false otherwise
  • signatureAlgorithm -- a description of the algorithm used to sign the certificate. Will be one of "md2WithRSAEncryption", "md5WithRSAEncryption", "sha1WithRSAEncryption", "sha256WithRSAEncryption", "sha384WithRSAEncryption", "sha512WithRSAEncryption", "ecdsaWithSHA1", "ecdsaWithSHA224", "ecdsaWithSHA256", "ecdsaWithSHA384", "ecdsaWithSHA512", or "unknown".
• disabledSHA1 -- true if SHA-1 was disabled, false otherwise
• didNotDisableSHA1Because -- a short string describing why SHA-1 could not be disabled, if applicable. Reasons are limited to:
  1. "MITM" if the user is behind a TLS intercepting proxy using a publicly-trusted root
  2. "connection error" if there was an error connecting to telemetry.mozilla.org
  3. "code error" if some inconsistent state was detected, and it was determined that the experiment should not attempt to change the preference
  4. "preference:userReset" if the user reset the SHA-1 policy after it had been changed by this add-on
  5. "preference:allow" if the user had already configured Firefox to always accept SHA-1 signatures
  6. "preference:forbid" if the user had already configured Firefox to always forbid SHA-1 signatures

For a connection not intercepted by a TLS proxy and where the user is in the test cohort, the expected result will be:

{ "cohortName": "test",
  "errorCode": 0,
  "error": "",
  "chain": [
    { "sha256Fingerprint": "197feaf3faa0f0ad637a89c97cb91336bfc114b6b3018203cbd9c3d10c7fa86c",
      "isBuiltInRoot": false,
      "signatureAlgorithm": "sha256WithRSAEncryption"
    },
    { "sha256Fingerprint": "154c433c491929c5ef686e838e323664a00e6a0d822ccc958fb4dab03e49a08f",
      "isBuiltInRoot": false,
      "signatureAlgorithm": "sha256WithRSAEncryption"
    },
    { "sha256Fingerprint": "4348a0e9444c78cb265e058d5e8944b4d84f9662bd26db257f8934a443c70161",
      "isBuiltInRoot": true,
      "signatureAlgorithm": "sha1WithRSAEncryption"
    }
  ],
  "disabledSHA1": true,
  "didNotDisableSHA1Because": ""
}

When this result is encountered, the user's preferences are updated to disable SHA-1 in signatures on certificates issued by publicly-trusted roots. Similarly, if the user is behind a TLS intercepting proxy but the root certificate is not part of the public web PKI, we can also disable SHA-1 in signatures on certificates issued by publicly-trusted roots.

If the user has already indicated in their preferences that they will always accept SHA-1 in signatures or that they will never accept SHA-1 in signatures, then the preference is not changed.