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SSLSocket.getpeercertchain() #62433
Description
| BPO | 18233 |
|---|---|
| Nosy | @jcea, @pitrou, @tiran, @ashemedai, @njsmith, @mmaker, @dstufft, @dsoprea, @miki725, @mmasztalerczuk, @chet, @joernheissler, @chrisburr, @JustAnotherArchivist, @jamespo |
| PRs | |
| Dependencies | |
| Files |
Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.
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GitHub fields:
assignee = 'https://github.com/tiran'
closed_at = None
created_at = <Date 2013-06-16.20:39:55.412>
labels = ['expert-SSL', 'type-feature', '3.10']
title = 'SSLSocket.getpeercertchain()'
updated_at = <Date 2021-06-21.15:17:12.858>
user = 'https://github.com/tiran'bugs.python.org fields:
activity = <Date 2021-06-21.15:17:12.858>
actor = 'jamespo'
assignee = 'christian.heimes'
closed = False
closed_date = None
closer = None
components = ['SSL']
creation = <Date 2013-06-16.20:39:55.412>
creator = 'christian.heimes'
dependencies = ['18147']
files = ['30611', '30622', '45057']
hgrepos = []
issue_num = 18233
keywords = ['patch']
message_count = 32.0
messages = ['191287', '191352', '193424', '199434', '199443', '199446', '199447', '203187', '203189', '203190', '205734', '244312', '244313', '244314', '278494', '280348', '293570', '293577', '293580', '293590', '293778', '301525', '324917', '357540', '361076', '361085', '361093', '361095', '361120', '372627', '372673', '391916']
nosy_count = 20.0
nosy_names = ['jcea', 'pitrou', 'christian.heimes', 'asmodai', 'njs', 'maker', 'Hiroaki.Kawai', 'underrun', 'zwol', 'dstufft', 'dsoprea', 'miki725', 'mmasztalerczuk', 'chet', 'joernheissler', 'chaen', 'chrisburr', 'kwatsen', 'JustAnotherArchivist', 'jamespo']
pr_nums = ['17938', '25467']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue18233'
versions = ['Python 3.10']
Activity
tiran commentedon Jun 16, 2013
The patch implements a method getpeercertchain() on a SSLSocket. It returns the peer's certificate chain from the leaf cert to the root cert if available. It wraps SSL_get_peer_cert_chain().
SSL_get_peer_cert_chain() doesn't have to pull any additional data from the peer. The information is already exchanged for cert validation.
tiran commentedon Jun 17, 2013
As expected it is much harder to get the full certification chain from OpenSSL than I initially expected. SSL_get_peer_cert_chain() doesn't return the root CA's certificate. The new patch introduces a validation mode and uses X509_verify_cert(*X509_STORE_CTX) + X509_STORE_CTX_get1_chain() to build a full chain.
tiran commentedon Jul 20, 2013
From Rietveld review:
---
http://bugs.python.org/review/18233/diff/8422/Modules/_ssl.c#newcode1203
Modules/_ssl.c:1203: chain = X509_STORE_CTX_get1_chain(store_ctx);
This isn't appropriate for this method. Specifically, you are asking for
the peer cert chain, which purposefully does not include root CA certs
that you trust. What you are giving here a complete validate chain from
a peer cert to a trusted root. This is a valuable piece of information,
but should be returned via another method (perhaps exposed in python as
get1chain in SSLContext). But this method should always return the
result of SSL_get_peer_cert_chain if a peer cert chain is available.
---
You are making a good point. I'm either going to split it up into two function or provide a way to look up a cert by issuer.
dsoprea commentedon Oct 11, 2013
I was about to submit a feature request to add exactly this. The [second] patch works like a charm. When are you going to land on a particular resolution so that it can get committed in?
Dustin
pitrou commentedon Oct 11, 2013
The patch needs a test, a proper doc, and reviewing.
pitrou commentedon Oct 11, 2013
Sorry for the incorrect answer. I just noticed there was a test in the patch!
Further looking at it, I notice the new function is returning a tuple. Wouldn't it be better to return a list here?
dsoprea commentedon Oct 11, 2013
My two-cents is to leave it a tuple (why not?).
Dustin
tiran commentedon Nov 17, 2013
I'd rather return a list or tuple of X509 objects but bpo-18369 won't be ready for 3.4. Ideas?
pitrou commentedon Nov 17, 2013
@dustin
Because tuples are more used for struct-like data. Here we are returning an unknown number of homogenous objects, which generally calls for a list.
@christian
Unless the feature is really important to have right now, I think it's ok to defer it until we have X509 objects.
tiran commentedon Nov 17, 2013
It's just nice to have for debugging and extended verification.
underrun commentedon Dec 9, 2013
I could really use this sooner than later... and sometimes having a full-featured (or even secure) interface is not what you want.
Consider zmap and masscan etc and ssl mapping (similar to what the EFF did a couple years back - https://www.eff.org/observatory - but with the full chain instead of just the cert). The desire here would be low level, low overhead, no validation on the fly: All you want is the cert chain.
There are plenty of research and security applications where a simple wrapper around OpenSSL that returns DER bytes would be desirable. Please reconsider this patch for inclusion in 3.4 ...
ashemedai commentedon May 28, 2015
Given that cryptography.io is fast becoming the solution for dealing with X.509 certificates on Python, I would like to add my vote to add my vote for this feature. Right now, getting the full chain in DER is what I am missing to complete a task at work.
dsoprea commentedon May 28, 2015
Forget it. This project is dead.
Dustin
On May 28, 2015 11:58 AM, "Jeroen Ruigrok van der Werven" <
report@bugs.python.org> wrote:
17 remaining items
kwatsen commentedon Jan 30, 2020
I don't understand the concern issues being raised for this patch, and also may have a use-case not mentioned yet.
For the concern issue, as I understand it, the ability to call getpeercert() or the proposed getpeercertchain() is only after the TLS session has been established. As such, the SSL socket already established that there exists a valid chain of trust. Thus these methods are primarily to provide visibility into what the peer passed *after* it had been authenticated, right?
That said, the reason I want to access the entire certificate chain passed by the client (i.e., client cert auth) is in order to validate that the client's cert (which may include some intermediates) authenticates to a specific trust anchor, rather than the bag of trust anchors loaded into the SSLContext (via load_verify_locations()) in order to authenticate a multiplicity of clients, each potentially leading to a different trust anchor.
Not having getpeercertchain() means that all no client cert may contain a chain, i.e., the clients only ever transmit the end-entity cert itself. This is unfortunate because the underlying SSL socket actually allows clients to send chains, it's just the lack being able to access the peercertchain in my code that seems to limit the solution.
njsmith commentedon Jan 31, 2020
The issue is that "the cert chain provided by the client" and "the cert chain that was validated as trustworthy" might be different. For example, say you have trust roots A and B, and I have a leaf certificate with a valid signature by B. If I pass the chain [A, leaf cert], then openssl's trust validation code might look at that and say "yep, this leaf cert is signed by root B, I trust root B, cool, the connection is good. Also there's a random A cert here, but whatever, that doesn't change anything".
In this case, for your use case, you want to get back the chain [B, leaf cert], because that's the chain that was actually validated. If you instead got the chain the client gave you, then you might be fooled into thinking that this cert chained to root A, when it actually didn't, and make the wrong trust decision.
That's why we need to be careful to distinguish between these two possible chains.
kwatsen commentedon Jan 31, 2020
It seems that we're talking about the same thing, but I want the cert-chain the peer sent without any smarts, exactly how OpenSSL's SSL_get_peer_cert_chain() works and, importantly, without stapling any root chain certs the client did not send itself (though it's okay if the client did, in which case those certs should be included).
I'm not following your "I pass the chain [A, leaf cert]" comment, if leaf-cert is signed by B, then this should obviously fail. Maybe you meant to say that A and B are loaded into a bag and that validation test is [bag, leaf-cert]?
Regardless, I don't think Python should coddle developers. Assuming the docs are accurate, competent developers with crypto-clue will be fine. Many crypto library docs encourage tourists to stay away. That said, if smarts are wanted, let's choose a name that doesn't overlap with the existing OpenSSL name...get_authed_cert_chain() ?
But, please, can a "peer_cert_chain()" wrapping the OpenSSL call be release ASAP, buying time to ponder the merits of smart calls for another day?
njsmith commentedon Jan 31, 2020
I'm not sure I agree about assuming that users will be able to work around these issues... I mean, nothing personal, I'm sure you're well-informed and maybe your code would work fine, but if you don't understand my example then how can you be entirely confident that you really understand all the risks that your code needs to watch out for?
Anyway, the proposed PR exposes both methods, so that's not a problem; it's just waiting on someone with openssl expertise like Christian to review it.
kwatsen commentedon Jan 31, 2020
I agree that having both would be best, but there is a world of difference between a must-have (peer_cert_chain) and what seems to be a nice-to-have (authed_peer_cert_chain).
My request for clarification was not that I don't understand bags, etc. (see my first message), but that I don't understand the concrete use case in mind. That is, when is it that the app-logic would differ because the EE cert validated using one path versus another?
To explain the 'must-have' better, imagine one peer sending [A, B, C], where 'A' is the EE cert, and the other peer having TA [F, E, D], where 'F' is the self-signed root TA and 'D' is the Issuer that signed 'C'. The complete chain is [A-F] and this is what the SSL-level code will use during the handshake. But post-handshake, without peer_chain_cert(), there is NO WAY for the app-logic to create a valid chain. This is broken, for the reason mentioned in my first message.
zwol commentedon Jun 29, 2020
I have yet another use case for the function implemented by this patch (i.e. retrieving the cert chain actually sent by the server, regardless of whether that gives a path to a trust anchor). I'm implementing a network forensics tool, and one of the situations it's supposed to detect is when a man-in-the-middle is attempting to substitute its own cert for a site's "legitimate" cert (yes, possibly having suborned a public CA in order to do so). To make all of the planned heuristics for this work correctly, I need to record exactly what came over the wire.
If it would be useful for me to dust off the patch and/or implement the _other_ function that people requested (retrieve the chain that OpenSSL concluded was a valid chain to an accepted trust anchor) I can probably scare up time to do so in the next week or two. I imagine it's too late for 3.8 patch releases at this point, but assuming I did this, could it make 3.9?
chrisburr commentedon Jun 30, 2020
Hi Zack, I've already opened a PR that is loosely based on this patch. If you have time to give it a review I'd appreciate the extra set of eyes.
#17938
tiran commentedon Apr 26, 2021
New changeset 666991f by Christian Heimes in branch 'master':
bpo-18233: Add internal methods to access peer chain (GH-25467)
666991f
sigmavirus24 commentedon Nov 15, 2022
@tiran let me know if I can lend a hand here. I'm also interested in finding a way to "backport" this to supported pythons even if as a PyPI module
felixfontein commentedon Dec 22, 2023
This apparently has been superseded by #109109.