5 ms·

Generally the cliche is about not implementing your own cryptographic algorithms. As long as they only implement existing algorithms and don't generate new ones

by lexman0 10y ago

Generally the cliche is about not implementing your own cryptographic algorithms. As long as they only implement existing algorithms and don't generate new ones, I don't think this applies.

rdeboo 10y ago
I used to think that; but I'm following Dan Boneh's crypto course on Coursera at the moment, and he specifically notes that you should not even try to implement known algorithms yourself (for production; you could do it ofcourse for the learning experience). The reason is that there are subtle attacks on the implementation, such as timing attacks, which can leak information.
- pornin 10y ago
  One of the point of the exercise is to provide constant-time implementations that provably do not leak such information. The hash functions, two AES, one DES/3DES, RSA and elliptic curve implementations in BearSSL have been written to be constant-time. I still have to write some document that explains how such things are done.
- mSparks 10y ago
  cant be any worse than openssl. they have all code running in constant time from the alpha version. Next comes making sure there are no buffer overflows. the code is stable and compatible. If everyone leaves it to someone else who does it exactly? Obviously not ready for use in production until its been audited. Remind me again where i can download an audited ssl implimentation?
  - BillinghamJ 10y ago
    > cant be any worse than openssl. Not sure I'd agree with that. OpenSSL is very far from perfect and obviously contains many many security bugs, but it also has a very long history of fixes, knowledge, etc. and has a large number of eyes on it. It's more of a known quantity than something new.
    - mSparks 10y ago
      well. actually looks better from the start: There is not a single malloc() call in all the library. In fact, the whole of BearSSL requires only memcpy(), memmove(), memcmp() and strlen() from the underlying C library. This makes it utterly portable even in the most special, OS-less situations. (On “big” systems, BearSSL will automatically use a couple more system calls to access the OS-provided clock and random number generator.) On big desktop and server OS, this feature still offers an interesting characteristic: immunity to memory leaks and memory-based DoS attacks. Outsiders cannot make BearSSL allocate megabytes of RAM since BearSSL does not actually know how to allocate RAM at all.
    - wbl 10y ago
      OpenSSL does not have half the fixes people think it does. Generally what gets fixed is the ciphersuites some people happen to use, and the rest remain broken. For example, the constant time ECDSA signing only works with some curves, not all. It still supports horrific hacks for random number generation, instead of using OS provided interfaces. NSS is not much better on this front, but does a far better job of parsing TLS records in a sane way.
  - deleted 10y ago
    [deleted]
- byuu 10y ago
  This thinking is why Heartbleed was such a disaster. Everyone left it to someone else, and the end result was OpenSSL being the only serious choice. Yet even the 'experts' got it wrong -- way wrong. I'm not advocating everyone and their mother implement their own crypto. But some software diversity is a good thing. These algorithms aren't quite as scary or fickle as the documentation and existing implementations make them seem. Especially if you stick to good software like DJB's stuff. For instance, using montgomery/edwards curves instead of weierstrass curves eliminates a lot of the difficulty in writing a constant-time implementation of ECC. And the 25519 implementation comes with a fast, constant-time implementation of a prime field type. Yet even DJB's stuff can be simplified. You can knock off a good 80% of the scary code at a cost of a mere 10% of performance. To Google or Facebook, that may be unacceptable. But to me, that's entirely worth it. Now you have a tiny library that is easy to understand, and easy to audit.
  - oconnor663 10y ago
    > Yet even DJB's stuff can be simplified. You can knock off a good 80% of the scary code at a cost of a mere 10% of performance. Wouldn't you say DJB (et al) did that themselves? https://tweetnacl.cr.yp.to/ https://tweetnacl.cr.yp.to/
    - byuu 10y ago
      I haven't benchmarked TweetNaCl's performance yet, but I think that goes way too far into making the code completely unreadable. The 80%/10% number I gave is against the ref10 implementation. Compare theirs: https://tweetnacl.cr.yp.to/20140427/tweetnacl.c https://tweetnacl.cr.yp.to/20140427/tweetnacl.c To mine: https://gitlab.com/higan/higan/blob/master/nall/elliptic-curve/curve25519.hpp https://gitlab.com/higan/higan/blob/master/nall/elliptic-cur... https://gitlab.com/higan/higan/blob/master/nall/elliptic-curve/ed25519.hpp https://gitlab.com/higan/higan/blob/master/nall/elliptic-cur... https://gitlab.com/higan/higan/blob/master/nall/cipher/chacha20.hpp https://gitlab.com/higan/higan/blob/master/nall/cipher/chach... https://gitlab.com/higan/higan/blob/master/nall/mac/poly1305.hpp https://gitlab.com/higan/higan/blob/master/nall/mac/poly1305... https://gitlab.com/higan/higan/blob/master/nall/hash/sha256.hpp https://gitlab.com/higan/higan/blob/master/nall/hash/sha256.... Please note that like BearSSL, my implementations are alpha-quality. Further, I'm not suggesting anyone use these in production. If I do so myself and it blows up in my face, it'll only have harmed me, and I'll only have myself to blame. (Also, I'm really bad when it comes to source code comments, sorry. The why really needs you to read the research papers; the how is mostly self-evident. The remaining one-letter variable names were used to match the papers, and because I couldn't think of more descriptive terms.)
- deleted 10y ago
  [deleted]
akie 10y ago
I still think it applies.
keymone 10y ago
this might give people false sense of security. implementing own crypto exposes you and those few souls that bought into your story. implementing bug-free "proven crypto" is near impossible task, but "proven crypto" part sells much better and so exposes many more un-expecting victims.
- throwawayReply 10y ago
  Nobody gets fired for linking openssl.
  - nine_k 10y ago
    ...yet. Not sure about 10 years from now.
user5994461 10y ago
Your own implementation of an algorithm is also a cliche. Use proven and battle tested library. You won't do any better on your own.
tptacek 10y ago
Whoah, no. It's about building crypto code at all. Given a choice between building something with Nacl and a bespoke stream cipher and building something with a bespoke cryptosystem and AES, I would have a hard time picking, but I'd lean towards Nacl.

by lexman0 10y ago

Generally the cliche is about not implementing your own cryptographic algorithms. As long as they only implement existing algorithms and don't generate new ones, I don't think this applies.

rdeboo 10y ago

I used to think that; but I'm following Dan Boneh's crypto course on Coursera at the moment, and he specifically notes that you should not even try to implement known algorithms yourself (for production; you could do it ofcourse for the learning experience). The reason is that there are subtle attacks on the implementation, such as timing attacks, which can leak information.

pornin 10y ago
One of the point of the exercise is to provide constant-time implementations that provably do not leak such information. The hash functions, two AES, one DES/3DES, RSA and elliptic curve implementations in BearSSL have been written to be constant-time. I still have to write some document that explains how such things are done.
mSparks 10y ago
cant be any worse than openssl. they have all code running in constant time from the alpha version. Next comes making sure there are no buffer overflows. the code is stable and compatible. If everyone leaves it to someone else who does it exactly? Obviously not ready for use in production until its been audited. Remind me again where i can download an audited ssl implimentation?
- BillinghamJ 10y ago
  > cant be any worse than openssl. Not sure I'd agree with that. OpenSSL is very far from perfect and obviously contains many many security bugs, but it also has a very long history of fixes, knowledge, etc. and has a large number of eyes on it. It's more of a known quantity than something new.
  - mSparks 10y ago
    well. actually looks better from the start: There is not a single malloc() call in all the library. In fact, the whole of BearSSL requires only memcpy(), memmove(), memcmp() and strlen() from the underlying C library. This makes it utterly portable even in the most special, OS-less situations. (On “big” systems, BearSSL will automatically use a couple more system calls to access the OS-provided clock and random number generator.) On big desktop and server OS, this feature still offers an interesting characteristic: immunity to memory leaks and memory-based DoS attacks. Outsiders cannot make BearSSL allocate megabytes of RAM since BearSSL does not actually know how to allocate RAM at all.
  - wbl 10y ago
    OpenSSL does not have half the fixes people think it does. Generally what gets fixed is the ciphersuites some people happen to use, and the rest remain broken. For example, the constant time ECDSA signing only works with some curves, not all. It still supports horrific hacks for random number generation, instead of using OS provided interfaces. NSS is not much better on this front, but does a far better job of parsing TLS records in a sane way.
- deleted 10y ago
  [deleted]
byuu 10y ago
This thinking is why Heartbleed was such a disaster. Everyone left it to someone else, and the end result was OpenSSL being the only serious choice. Yet even the 'experts' got it wrong -- way wrong. I'm not advocating everyone and their mother implement their own crypto. But some software diversity is a good thing. These algorithms aren't quite as scary or fickle as the documentation and existing implementations make them seem. Especially if you stick to good software like DJB's stuff. For instance, using montgomery/edwards curves instead of weierstrass curves eliminates a lot of the difficulty in writing a constant-time implementation of ECC. And the 25519 implementation comes with a fast, constant-time implementation of a prime field type. Yet even DJB's stuff can be simplified. You can knock off a good 80% of the scary code at a cost of a mere 10% of performance. To Google or Facebook, that may be unacceptable. But to me, that's entirely worth it. Now you have a tiny library that is easy to understand, and easy to audit.
- oconnor663 10y ago
  > Yet even DJB's stuff can be simplified. You can knock off a good 80% of the scary code at a cost of a mere 10% of performance. Wouldn't you say DJB (et al) did that themselves? https://tweetnacl.cr.yp.to/ https://tweetnacl.cr.yp.to/
  - byuu 10y ago
    I haven't benchmarked TweetNaCl's performance yet, but I think that goes way too far into making the code completely unreadable. The 80%/10% number I gave is against the ref10 implementation. Compare theirs: https://tweetnacl.cr.yp.to/20140427/tweetnacl.c https://tweetnacl.cr.yp.to/20140427/tweetnacl.c To mine: https://gitlab.com/higan/higan/blob/master/nall/elliptic-curve/curve25519.hpp https://gitlab.com/higan/higan/blob/master/nall/elliptic-cur... https://gitlab.com/higan/higan/blob/master/nall/elliptic-curve/ed25519.hpp https://gitlab.com/higan/higan/blob/master/nall/elliptic-cur... https://gitlab.com/higan/higan/blob/master/nall/cipher/chacha20.hpp https://gitlab.com/higan/higan/blob/master/nall/cipher/chach... https://gitlab.com/higan/higan/blob/master/nall/mac/poly1305.hpp https://gitlab.com/higan/higan/blob/master/nall/mac/poly1305... https://gitlab.com/higan/higan/blob/master/nall/hash/sha256.hpp https://gitlab.com/higan/higan/blob/master/nall/hash/sha256.... Please note that like BearSSL, my implementations are alpha-quality. Further, I'm not suggesting anyone use these in production. If I do so myself and it blows up in my face, it'll only have harmed me, and I'll only have myself to blame. (Also, I'm really bad when it comes to source code comments, sorry. The why really needs you to read the research papers; the how is mostly self-evident. The remaining one-letter variable names were used to match the papers, and because I couldn't think of more descriptive terms.)
deleted 10y ago
[deleted]

akie 10y ago

I still think it applies.

keymone 10y ago

this might give people false sense of security. implementing own crypto exposes you and those few souls that bought into your story. implementing bug-free "proven crypto" is near impossible task, but "proven crypto" part sells much better and so exposes many more un-expecting victims.

throwawayReply 10y ago
Nobody gets fired for linking openssl.
- nine_k 10y ago
  ...yet. Not sure about 10 years from now.

user5994461 10y ago

Your own implementation of an algorithm is also a cliche. Use proven and battle tested library. You won't do any better on your own.

tptacek 10y ago

Whoah, no. It's about building crypto code at all. Given a choice between building something with Nacl and a bespoke stream cipher and building something with a bespoke cryptosystem and AES, I would have a hard time picking, but I'd lean towards Nacl.