~dbalan/blogng unlisted

7d954673fe20475cb8bb535b39b3cfbf8a1a3ccc — Dhananjay Balan 11 months ago c496126
OCSP blog posts, some minor spell fixes.
2 files changed, 14 insertions(+), 11 deletions(-)

M blog/2019-08-06-trouble-with-ocsp.markdown
M css/theme.css
M blog/2019-08-06-trouble-with-ocsp.markdown => blog/2019-08-06-trouble-with-ocsp.markdown +10 -11
@@ 5,14 5,13 @@ date: 2019-08-06
comments: true
tags: ocsp, tor, security, privacy
---
# Trouble with OCSP

> This is a post about side channel information leakage that was present in OnionBrowser in some OCSP flows. This is not a exhaustive documentation of OCSP protocol.
> This is a post about side channel information leakage that was present in OnionBrowser in some OCSP flows. This post omits a lot of details about OCSP protocol.

Digital certificates are issued for a longer timespan. It reduces maintaince overhead. Most of the cases CAs issue a certificate and they are valid untill the expiration time.
Digital certificates are issued for a longer timespan. It reduces maintenance overhead. Most of the cases CAs issue a certificate and they are valid until the expiration time.

But what are we to do when a certificate is compromised? We can
re-issue a certificate, but the old one is still in the wind. Thats
re-issue a certificate, but the old one is still in the wind. That's
where Online Certificate Status Protocol comes in. It defines a way to
check validity of a certificate in a timely[^1] manner.



@@ 30,7 29,7 @@ the certificate itself, removing the need for another seperate
request.

## Dissecting an OCSP Request
If the request is <255 bytes, OCSP allows it to be passed as a GET path. So a typical request looks like this
If the request is <255 bytes, OCSP allows it to be passed as a GET path. A typical request looks like this

```bash
GET http://ocsp.int-x3.letsencrypt.org/MFgwVqADAgEAME8wTTBLMAkGBSsOAwIaBQAEFH7maudymrP8%2BKIgZGwWoS1gcQhdBBSoSmpjBH3duubRObemRWXv86jsoQISA6D%2BPqgUVCy3wtolHIxq%2Bk0e


@@ 77,7 76,7 @@ curl https://crt.sh/?serial=03a0fe3ea814542cb7c2da251c8c6afa4d1e
## Privacy Takes a Backseat.

Careful examination of above workflow will reveal that the OCSP flow
is happening over HTTP. Most issuers seems to stick to http; possibly
is happening over HTTP. Most issuers seem to stick to http; possibly
to avoid cyclical dependencies. This means man-in-the-middle leakage
of certificates a user is validating is happening, and by extension
leakage of websites user is accessing.


@@ 97,11 96,11 @@ Whenever Onion Browser accesses a website with EV cert, (for e.g

I stumbled upon this accidently while inspecting requests from my
iPhone with [mitmproxy](https://mitmproxy.org/). The bug was reported
to Onion Browser team and [they have a better write up of the
situation](https://github.com/OnionBrowser/OnionBrowser/wiki/2019-178:-sites-with-EV-HTTPS-certificates-leak-information-via-OCSP). Unfortunatly
it is really hard to fix. :-(
to Onion Browser team and [they have a nice write up of the
situation](https://github.com/OnionBrowser/OnionBrowser/wiki/2019-178:-sites-with-EV-HTTPS-certificates-leak-information-via-OCSP). Unfortunately,
it is hard to fix. :-(



[^1]: Opposed to checking againist a [Certificate Revocation List](https://en.wikipedia.org/wiki/Certificate_revocation_list).
[^2]: Familier readers will note that this is plain OCSP, the non-stapling kind.
[^1]: Opposed to checking against a [Certificate Revocation List](https://en.wikipedia.org/wiki/Certificate_revocation_list).
[^2]: Familiar readers will note that this is plain OCSP, the non-stapling kind.

M css/theme.css => css/theme.css +4 -0
@@ 37,6 37,10 @@ body {
    text-align: left;
}

blockquote {
    font-style: italic;
}

video, code {
    font-weight: 500;
    max-width: 100%;