Mailman 3 February 2018 - Cryptography-dev

Failed: Cryptography (96787f95)
by Read the Docs Feb. 25, 2018

Feb. 25, 2018

Build Failed for Cryptography (latest) You can find out more about this failure here: https://readthedocs.org/projects/cryptography/builds/6801082/ If you have questions, a good place to start is the FAQ: https://docs.readthedocs.org/en/latest/faq.html Keep documenting, Read the Docs -- http://readthedocs.org

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Failed: Cryptography (8374206d)
by Read the Docs Feb. 25, 2018

Feb. 25, 2018

Build Failed for Cryptography (latest) You can find out more about this failure here: https://readthedocs.org/projects/cryptography/builds/6799808/ If you have questions, a good place to start is the FAQ: https://docs.readthedocs.org/en/latest/faq.html Keep documenting, Read the Docs -- http://readthedocs.org

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Failed: Cryptography (404496ae)
by Read the Docs Feb. 23, 2018

Feb. 23, 2018

Build Failed for Cryptography (latest) You can find out more about this failure here: https://readthedocs.org/projects/cryptography/builds/6795481/ If you have questions, a good place to start is the FAQ: https://docs.readthedocs.org/en/latest/faq.html Keep documenting, Read the Docs -- http://readthedocs.org

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Re: [Cryptography-dev] Cryptography-dev Digest, Vol 54, Issue 5
by Andrew W. Donoho Feb. 23, 2018

Feb. 23, 2018

> On Feb 23, 2018, at 11:00 , cryptography-dev-request(a)python.org wrote: > > However, as several others have explained, this does not prevent the memory > getting stored on the disk in some manner. tux, You are absolutely correct. Prudence is required. Your advice to skeptically believe that I have fully protected myself from key snooping is noted and embraced. Note that I am attempting to make the key's exposure last for as short a time as possible. Certainly you support this goal? I ask each cloud vendor what their VM swap encryption policy is. Some claim that just their disks are encrypted. That encrypted swap is not necessary. These are also the same folks who believe secrets are safe as environment variables. (*cough* Docker *cough* Heroku *cough*) At least AWS is now offering explicitly secure secret parameters. Yes, we should know exactly what are the swap and encryption policies of each of the function execution environment vendors. When pressed at conferences like OSCON, these vendors fall back upon the “Top Men” argument. They employ “Top Men” who never make mistakes. (Nor will the org stand behind them not making mistakes.) BTW, this is the same “Top Men” defense offered by AWS when I ask to see the results of any third party security audit of Boto3, the AWS access library. I hope their “Top Men” are truly “Top Men.” More transparency would be welcome. In particular, I’ve inquired of the AWS Encryption SDK team how they control the lifetime of their cached, unencrypted credentials. They did not have a good solution nor did they explicitly address exposed key lifetimes. I believe a member of that team has already participated in this thread. For which I thank him. Here’s a critical patch notice: Amazon Linux AMI Security Advisory: ALAS-2018-939, <https://alas.aws.amazon.com/ALAS-2018-939.html <https://alas.aws.amazon.com/ALAS-2018-939.html>>. Clearly, this threat of cross process snooping is taken seriously by AWS and, I assume, will soon be addressed in their other services. One assumes this would be done relatively quickly for the AWS Encryption SDK. I assume each of the cloud vendors views Meltdown with similar concern. I, as a user, have a responsibility too. I should not leave unencrypted key material lying around my address space. That is why I use specialized services that exploit hardware security modules. Hence, I’ve come here to address the exposed key problem myself instead of depending upon the AWS Encryption SDK. This open and engaged community has rewarded my effort. Thank you. More folks should be asking for public disclosure of these important security policies. In my case, I am attempting to precisely control the lifetime of these secrets. I am attempting to minimize the time I am exposed. With the advice and guidance of this team, I feel I can now track the explicit lifetime and disposition of my EC and AES secrets. I’ll leave password strings to another time. BTW, gc.collect(generation=0) has surprisingly little impact on my test routine’s execution speeds. It appears to properly cause the collection of my ec.privateKey. In other words, once again, the pyca/cryptography team has implemented their system well. Bravo! Anon, Andrew ____________________________________ Andrew W. Donoho Donoho Design Group, L.L.C. andrew.donoho(a)gmail.com, +1 (512) 666-7596, twitter.com/adonoho No risk, no art. No art, no reward. -- Seth Godin

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Re: [Cryptography-dev] Destroying keys and secrets?
by Andrew W. Donoho Feb. 22, 2018

Feb. 22, 2018

> On Feb 20, 2018, at 11:00 , cryptography-dev-request(a)python.org wrote: > > ec.derive_private_key_from_bytes(secret_bytes, ec.SECP384R1(), backend) > could potentially be a way to do this specific operation while reducing the > number of copies (to zero in Python and 2-3 in OpenSSL, although the latter > are zeroed), but without tests that can detect non-required copies of > secret material it would be extremely hard to prevent regression in the > long term as the code is updated. Paul, Based upon your hint above I just went in to the code and looked around. It looks like a straightforward extension. Note: I am not a library developer and, hence, have not developed all of the various skills to properly build pyca/cryptography. Nor am I particularly knowledgable about Python v2.7 & v3.6 interoperation issues, much less CPython, Cython and PyPy interoperation. The below code is a gedanken exploration to see how hard or involved it might actually be to extend pyca/cryptography. TL;DR: It isn’t hard. I C&P three functions and then modded them. Gratz to the team on an excellent design. It is clear that I could deploy my own copy of cryptography and call it a day. But I believe that key hygiene is an important social good. I am happy to help look at/write each routine that imports key material and propose versions that allow good key hygiene. As you note above, there is no solution for your regression testing issue except to discuss it in code commentary. Now to find a routine that can bang the contents of a bytes array to 0, 1 and then random. Should I proceed to engage with your team or just continue on my merry way? I want to help but if it isn’t something the team prioritizes highly right now, I fully understand. Anon, Andrew ____________________________________ Andrew W. Donoho Donoho Design Group, L.L.C. andrew.donoho(a)gmail.com, +1 (512) 666-7596, twitter.com/adonoho No risk, no art. No art, no reward. -- Seth Godin ===== backend.py ===== def _bytes_to_bn(self, num, bn=None): # Was: def _int_to_bn(self, num, bn=None): """ Converts a python bytes array to a BIGNUM. The returned BIGNUM will not be garbage collected (to support adding them to structs that take ownership of the object). Be sure to register it for GC if it will be discarded after use. """ assert bn is None or bn != self._ffi.NULL if bn is None: bn = self._ffi.NULL bn_ptr = self._lib.BN_bin2bn(num, len(num), bn) self.openssl_assert(bn_ptr != self._ffi.NULL) return bn_ptr def derive_elliptic_curve_private_key_bytes(self, private_bytes, curve): # Was: def derive_elliptic_curve_private_key(self, private_value, curve): curve_nid = self._elliptic_curve_to_nid(curve) ec_cdata = self._lib.EC_KEY_new_by_curve_name(curve_nid) self.openssl_assert(ec_cdata != self._ffi.NULL) ec_cdata = self._ffi.gc(ec_cdata, self._lib.EC_KEY_free) get_func, group = self._ec_key_determine_group_get_func(ec_cdata) point = self._lib.EC_POINT_new(group) self.openssl_assert(point != self._ffi.NULL) point = self._ffi.gc(point, self._lib.EC_POINT_free) value = self._bytes_to_bn(private_bytes) value = self._ffi.gc(value, self._lib.BN_clear_free) with self._tmp_bn_ctx() as bn_ctx: res = self._lib.EC_POINT_mul(group, point, value, self._ffi.NULL, self._ffi.NULL, bn_ctx) self.openssl_assert(res == 1) bn_x = self._lib.BN_CTX_get(bn_ctx) bn_y = self._lib.BN_CTX_get(bn_ctx) res = get_func(group, point, bn_x, bn_y, bn_ctx) self.openssl_assert(res == 1) res = self._lib.EC_KEY_set_public_key(ec_cdata, point) self.openssl_assert(res == 1) private = self._bytes_to_bn(private_bytes) private = self._ffi.gc(private, self._lib.BN_clear_free) res = self._lib.EC_KEY_set_private_key(ec_cdata, private) self.openssl_assert(res == 1) evp_pkey = self._ec_cdata_to_evp_pkey(ec_cdata) return _EllipticCurvePrivateKey(self, ec_cdata, evp_pkey) ===== ec.py ===== def derive_private_key_bytes(private_value, curve, backend): # Was: def derive_private_key(private_value, curve, backend): if not isinstance(curve, EllipticCurve): raise TypeError("curve must provide the EllipticCurve interface.") return backend.derive_elliptic_curve_private_key_bytes(private_value, curve)

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Re: [Cryptography-dev] Destroying keys and secrets?
by Andrew W. Donoho Feb. 21, 2018

Feb. 21, 2018

> On Feb 20, 2018, at 11:00 , cryptography-dev-request(a)python.org wrote: > Date: Mon, 19 Feb 2018 17:14:25 -0800 > From: Paul Kehrer <paul.l.kehrer(a)gmail.com> > To: cryptography-dev(a)python.org > Subject: Re: [Cryptography-dev] Cryptography-dev Digest, Vol 54, Issue > 2 > Message-ID: > <CABj5TKTv8cP6XGdCrABxF6qXJNZoipufe6_xy2y_N+R95KSuTA(a)mail.gmail.com> > Content-Type: text/plain; charset="utf-8” > > Access to Python's memory (via side channel or dumping as root) is not part > of pyca/cryptography's threat model at this time so we don't attempt to > protect against it. Making it part of our threat model would be difficult > due in part to the reasons you stated above as well as the difficulty in > writing tests to prevent regression, but let's talk about what CPython does > in this case. Paul, Thank you for your enlightening comments above and below. What Am I Really Trying To Do?: This function is initially an AWS lambda function that I also intend to support on Google Cloud and MS Azure. This august group of engineers obviously knows of my concern but I nonetheless wish to emphasize the problem. Perhaps I can also contribute to its solution? While I have control of the function’s environment, I don’t have total control. For example, while I can hope the host OS has enough entropy in its pool to support os.urandom(), the AWS recommendation, with which I concur, is that I get my random_bytes from the AWS KMS service and stir it up with an HKDF. As in: random_bytes = os.urandom(512//8) # <= Should come from AWS KMS random bytes service. # Derive a SECP384R1 private key using SHA-512, _salt512, and guid. hkdf = HKDF(algorithm=sha512, length=384//8, salt=_salt512, info=guid, backend=backend) secret_bytes = hkdf.derive(random_bytes) secret_int = int.from_bytes(secret_bytes, byteorder='big') private_key = ec.derive_private_key(secret_int, ec.SECP384R1(), backend) As I understand it, each of the cloud vendors offers a high entropy source of random bytes. Upon completion of this function, I want to scrub RAM of key material. I will never get another chance to address the existence of this key material. There is no goodbye kiss from the cloud function execution environments. These are one-shot function calls. If I am to ensure that this crypto toxic waste doesn’t come back to bite my service, then I must dispose of it in the function context that created it. In other words, pyca/cryptography is likely to be used in a much more dynamic environment than heretofore. Considering that pyca/cryptography has largely succeeded in building a civilized interface to crypto routines, helping folks implement good secret/key hygiene seems in scope for the project’s goals. Considering Amazon’s embrace of pyca/cryptography for their Python lambda functions and AWS Encryption SDK, I am unlikely to be the sole user. > int.from_bytes will unfortunately make a copy (to a Python integer). That > int will then be copied into a BN via _int_to_bn ( > https://github.com/pyca/cryptography/blob/master/src/cryptography/hazmat/ba…) > when you call derive_private_key. It will actually be converted twice (a > thing we should fix) ( > https://github.com/pyca/cryptography/blob/master/src/cryptography/hazmat/ba…). > Although the resulting BNs will themselves be zeroed as freed, this means a > secret scalar bytestring created in Python will be resident in memory no > less than 5 times (3 byte strings, 2 numbers). > > Obviously the next logical question is why you'd provide a Python integer > when we're just going to convert it back to big endian bytes anyway. > Disregarding the memory clearing issue it's also inefficient. When > originally designing some of the APIs we made a mistake and chose integers > instead of big endian bytes (see: numbers classes). We have not yet added > alternate APIs to potentially enable us to deprecate numbers because the > improvement in efficiency probably isn't worth the pain of trying to > convert the huge number of users of those classes. > > ec.derive_private_key_from_bytes(secret_bytes, ec.SECP384R1(), backend) > could potentially be a way to do this specific operation while reducing the > number of copies (to zero in Python and 2-3 in OpenSSL, although the latter > are zeroed), but without tests that can detect non-required copies of > secret material it would be extremely hard to prevent regression in the > long term as the code is updated. Thank you for the above excellent exposition of the state of data copying in pyca/cryptography. Considering the appropriate "stürm und drang" that accompanied Meltdown, Specter, and other exploits around key material, I think many developers have an interest in making the changes to their code that allows them to ensure precise key material lifetimes. Of course, with modern internet survey tools, the pyca/cryptography team can easily ask their users if they would make these changes. To your point about regression testing the copying of key material: I place this in the category of expertise of the library developer. There are plenty of similar cryptographic issues that the pyca/cryptography team has had to tackle through discipline and intra-project communication. Obviously, because your team already clears and then frees items passed to and from OpenSSL, you know how to do this. How can I help? I also note that ec.derive_private_key() has a paired routine where pyca/cryptography takes responsibility for the secret_bytes: ec.generate_private_key(). If it manages its secret copies carefully, I might consider using it instead of providing my own secret_bytes. It would, of course, depend upon pyca/cryptography’s high entropy data source (os.urandom()?). As this is in the hazmat section of the library, perhaps a discussion in the documentation about digital toxic/hazardous waste is appropriate? How can I help? > Given your chosen constraints have you considered deriving a key in > subprocess, serializing it, and reading it from stdout in the parent > process? By doing this you'd have a precisely defined intermediate object > lifetime and the only secret in the parent process's memory would be a > single DER or PEM bytestring containing the EC key. That is one excellent way to achieve my goal in a normal execution environment. All of the industry trends lead me to believe that AWS lambda function-like environments will become a high percentage of where crypto operations are performed. Due to their small scope and statelessness, they lend themselves to focussed and highly tuned solutions. They are a natural place for the cryptographic core functions of many systems to reside. Put all of your keys in one basket and then watch that basket very carefully. Thank you for taking the time to examine my concerns. Anon, Andrew ____________________________________ Andrew W. Donoho Donoho Design Group, L.L.C. andrew.donoho(a)gmail.com, +1 (512) 666-7596, twitter.com/adonoho No risk, no art. No art, no reward. -- Seth Godin

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Re: [Cryptography-dev] Cryptography-dev Digest, Vol 54, Issue 2
by Andrew W. Donoho Feb. 20, 2018

Feb. 20, 2018

> On Feb 17, 2018, at 11:00 , cryptography-dev-request(a)python.org wrote: > > Date: Sat, 17 Feb 2018 04:04:00 +0100 > From: Alex <python-cryptography(a)qu3.org> > To: cryptography-dev(a)python.org > Subject: Re: [Cryptography-dev] Destroying keys and secrets? > Message-ID: <d057417f-ce19-1a60-4d18-18680c56279a(a)nigl.biz> > Content-Type: text/plain; charset="utf-8" > > You might have a look at: > https://github.com/dnet/pysecstr > > Here is a longer description about the used method: > https://www.sjoerdlangkemper.nl/2016/06/09/clearing-memory-in-python/ > > Disclaimer: This is not a recommendation just a hint for further > exploration. Be also aware that you can't control if and when Python > swaps memory to disk. > On Feb 16, 2018, at 16:44 , cryptography-dev-request(a)python.org wrote: > Date: Fri, 16 Feb 2018 21:54:23 +0000 > From: Matt Bullock <matt.s.b.42(a)gmail.com> > To: cryptography-dev(a)python.org > Subject: Re: [Cryptography-dev] Destroying keys and secrets? > > I've also toyed with the idea of making a C extension analogous to the > SecretKey structure from Java, which never lets the actual key material out > of the structure, but in order to actually do anything with the key > material it still needs to surface to Python at some point, which puts us > back in the same position we started with. ..unless we were to re-implement > all of pyca/cryptography in Cython, but that's a thought for a different > time… > On Feb 16, 2018, at 16:44 , cryptography-dev-request(a)python.org wrote: > > Date: Fri, 16 Feb 2018 15:44:39 -0700 > From: John Pacific <me(a)johnpacific.com> > To: cryptography-dev(a)python.org > Subject: Re: [Cryptography-dev] Destroying keys and secrets? > Message-ID: > <CAHr1PUP6Wvzdho02YfoZg4mWttdz3CXRkPjssBUJ1wtLuPUBYQ(a)mail.gmail.com> > Content-Type: text/plain; charset="utf-8" > > Afaik, there is no reliable way to do this in Python. > > I have taken some time to implement some OpenSSL methods that at least > clear the memory on private numbers before freeing it in BIGNUMBER > operations. > > See the PR here: https://github.com/pyca/cryptography/pull/4072 > > However, as it comes for the Elliptic curve Gentlemen, Thank you for your fine answers. They comport with my expectations. Without boring you with my details, I am doing something similar to an ephemeral ECDH exchange. The secrets have a very short lifetime. Hence, I’m not worried about swapping to disk. (Though most of the cloud vendors claim the swap vm is encrypted.) For example: secret_bytes = os.urandom(384//8) secret_int = int.from_bytes(secret_bytes, byteorder='big') private_key = ec.derive_private_key(secret_int, ec.SECP384R1(), backend) I would like secret_bytes, secret_int, and private_key to be zeroed-out before I exit the function. I want as precise an object lifetime as possible. While I fully understand the values of a library maintainer wishing to have a robust solution for all supported versions and runtimes, I have explicit control of this function and its execution environment. I’m more concerned about revealing the secret in a hostile cloud. In particular, I don’t have the string aliasing problem. Yes, this is a fragile and extremely hazardous solution. OTOH, the industry just freaked out about Meltdown. It behooves us all to manage key lifetimes carefully. As I dig into examining this problem further, I assume the ec.derive_private_key() function takes a conservative approach and doesn’t ever copy the secret_int? If I’m living well, banging the bytes in secret_bytes might hit the only copy of the secret. Depends upon whether int.from_bytes() copies the storage of an immutable source. Again, thank you for your answers. I’ll keep you posted with my progress. Anon, Andrew ____________________________________ Andrew W. Donoho Donoho Design Group, L.L.C. andrew.donoho(a)gmail.com, +1 (512) 666-7596, twitter.com/adonoho No risk, no art. No art, no reward. -- Seth Godin

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Destroying keys and secrets…
by Andrew Donoho Feb. 17, 2018

Feb. 17, 2018

Gentlefolk, Apparently, my Google-fu is weak and I come seeking advice. Secret management is important. In particular, I want to make sure that any secrets I decrypt are erased from memory before the storage is reclaimed by the VM. In other environments, I would just dig into each object until I get the pointer for the storage and then bang zeros, ones and randomness into the block. Then garbage collection would proceed apace. Here’s an example from the cryptography documentation, <https://cryptography.io/en/latest/hazmat/primitives/symmetric-encryption/>: >>> import os >>> from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes >>> from cryptography.hazmat.backends import default_backend >>> backend = default_backend() >>> key = os.urandom(32) >>> iv = os.urandom(16) >>> cipher = Cipher(algorithms.AES(key), modes.CBC(iv), backend=backend) >>> encryptor = cipher.encryptor() >>> ct = encryptor.update(b"a secret message") + encryptor.finalize() >>> decryptor = cipher.decryptor() >>> decryptor.update(ct) + decryptor.finalize() 'a secret message’ The `key` above is a `bytes` object. It has storage somewhere. Even though it is a read-only Python object, I can pierce the abstraction, if I have to, with C. My question is: has someone else already done so and published the handful of methods needed? If not, should this be an API added to cryptography? Anon, Andrew ____________________________________ Andrew W. Donoho Donoho Design Group, L.L.C. awd(a)DDG.com, +1 (512) 750-7596, twitter.com/adonoho Doubt is not a pleasant condition, but certainty is absurd. — Voltaire

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