Cryptography

为什么我们提供密码系统?

简单的说: 因为我们有这个能力。

OpenBSD 项目基地设在加拿大。

加拿大出口控制列表没有对密码学软件的出口设置特别的限制性条款， 甚至明文规定允许自由出口自由的密码学软件。Marc Plumb 已经做了一些研究来验证相关的法律。

因此，OpenBSD 项目把密码学技术嵌入了操作系统的很多地方。 我们要求所使用的加密软件可以免费获取并拥有良好版权许可。 我们不会直接使用那些带有令人厌恶的专利权的加密软件。 我们还要求这些软件是从有出口许可的国家输出的， 因为我们并不想违反任何国家的法律。 我们当前使用的密码学软件组件来自阿根廷，澳大利亚，加拿大，德国，希腊, 挪威和瑞士。

当我们制作 OpenBSD 发行版本和快照版本的时候， 我们在允许自由输出的国家来完成， 以保证我们提供的源码和二进制代码可以被用户自由使用。 在过去，我们提供的编译好的版本是在加拿大，瑞士和德国完成的。

OpenBSD 包含了 Kerberos V。其基本代码来自瑞士的可以出口的 Heimdal 版本。 我们的 X11 源码也已经扩展到可以使用 Kerberos 验证机制了

OpenBSD 是第一个带 IPsec 栈的操作系统。我们从1997年发行的 OpenBSD 2.1 版本就开始带 IPsec。我们完全内嵌在内核里面的 IPsec 栈， 加上可基于多种卡的硬件加速，以及我们自由的 ISAKMP 守护进程, 被用于 VPNC 中的一些 IPsec 兼容性测试主机。

今天，密码学技术成为了增强操作系统安全性的一个重要手段。 OpenBSD 中对密码学技术的利用可以分为以下几个方面。

OpenSSH

从版本 2.6 开始，OpenBSD 包含 OpenSSH，一个完全自由免费，没有任何专利权限制的 ssh 实现。 OpenSSH 除了兼容 ssh 版本 1 之外还增加了很多新特性：

• 所有受限制的组件(也就是专利权，参见 ssl(8)) 都已被直接从源码中去除掉；任何有版权或者专利权的软件用外部函数库的形式提供。
• 已经更新到支持 ssh 协议 2。
• 增加对 Kerberos 验证和票据传递的支持
• 支持使用 skey(1) 进行一次性密码验证。

粗略的说，我们发行的是 OpenBSD 自由的兼容版 ssh。大约过了一年后，我们把 OpenSSH 扩展至支持 SSH 2 协议，从而 OpenSSH 就可以支持所有主要的 3 个 SSH 协议: 1.3，1.5 和 2.0。

伪随机数生成器

伪随机数生成器(PRNG)为应用程序提供数字流，并且为系统安全提供了重要的特性:

• 对外界来说，即使知道上次的输出，也不可能推测出随机数生成器下次的输出。
• 产生的数字不应该有重复模式，这意味着 PRNG 应该有很长的周期。

PRNG 通常只是算法，相同的初始值将产生同样的输出序列。 在一个多用户操作系统上，有很多来源为 PRNG 产生种子。 OpenBSD 内核使用鼠标中断时间，网络数据中断延时，键盘按键间隔时间， 和磁盘 IO 信息来填充熵池。内核例程可以读取随机数， 而且也通过设备输出到了用户空间程序。到目前为止，随机数用于如下场合:

• Dynamic sin_port allocation in bind(2).
• PIDs of processes.
• IP datagram IDs.
• RPC transaction IDs (XID).
• NFS RPC transaction IDs (XID).
• DNS Query-IDs.
• Inode generation numbers, see getfh(2) and fsirand(8).
• Timing perturbance in traceroute(8).
• Stronger temporary names for mktemp(3) and mkstemp(3)
• Randomness added to the TCP ISS value for protection against spoofing attacks.
• random padding in IPsec esp_old packets.
• To generate salts for the various password algorithms.
• For generating fake S/Key challenges.
• In isakmpd(8) to provide liveness proof of key exchanges.

密码学散列函数

散列函数在接收输入的数据后，将其压缩到一个恒定的大小。 对散列函数来说，不可能出现以下情况:

• 两个输入产生同样的输出(抵抗冲突)，
• 对于一个给定的输入，找到一个不同的输入得到了相同的输出(抵抗前象)。

在 OpenBSD 中，MD5，SHA1，和 RIPEMD-160 用于散列函数，举例来说:

• In S/Key(1) to provide one time passwords.
• In IPsec(4) and isakmpd(8) to authenticate the data origin of packets and to ensure packet integrity.
• For FreeBSD-style MD5 passwords (not enabled by default), see passwd.conf(5)
• In libssl for digital signing of messages.

密码学变换

密码学变换被用于数据的加密和解密。通常是一个加密密钥用于数据加密， 一个解密密钥用作数据的解密。一个密码学变换的安全性取决于密钥自身。

OpenBSD 提供了 DES, 3DES, Blowfish 和 Cast 用于内核与用户空间的程序， 它们用于许多场合，例如:

• In libc for creating Blowfish passwords. See also the USENIX paper on this topic.
• In IPsec(4) to provide confidentiality for the network layer.
• In isakmpd(8) to protect the exchanges where IPsec key material is negotiated.
• In AFS to protect the messages passing over the network, providing confidentiality of remote filesystem access.
• In libssl to let applications communicate over the de-facto standard cryptographically secure SSL protocol.

对密码系统硬件的支持

从 OpenBSD 2.7 开始支持一些密码系统硬件，比如加速器和随机数生成器。

• IPsec crypto dequeue
  Our IPsec stack has been modified so that cryptographic functions get done out-of-line. Most simple software IPsec stacks need to do cryptography when processing each packet. This results in synchronous performance. To use hardware properly and speedily one needs to separate these two components, as we have done. Actually, doing this gains some performance even for the software case.

• Hifn 7751
  Cards using the Hifn 7751 can be used as a symmetric cryptographic accelerator, i.e., the Soekris VPN1201 or VPN1211 ( to buy) or PowerCrypt. Current performance using a single Hifn 7751 on each end of a tunnel is 64Mbit/sec for 3DES/SHA1 ESP, nearly a 600% improvement over using a P3/550 CPU. Further improvements are under way to resolve a few more issues, but as of April 13, 2000 the code is considered stable. We wrote our own driver for supporting this chip, rather than using the (USA-written) PowerCrypt driver, as well our driver links in properly to the IPsec stack. The 7751 is now considered slow by industry standards and many vendors have faster chips (even Hifn now has a faster but more expensive chip). Peak performance with 3DES SHA1 ESP is around 64Mbit/sec.

  After 2.9 shipped, support was added for the Hifn 7951 chip, a simplified version of the 7751 which adds a public key accelerator (unsupported) and a random number generator (supported). Cards were donated by Soekris Engineering.

  After 3.0 shipped, support was added for the Hifn 7811 chip, a faster version of the 7751 (around 130Mbit/s) with a random number generator. A card was donated by GTGI.

  After 3.2 shipped, support was added for the LZS compression algorithm used by ipcomp(4).

  After 3.4 shipped, support was added for the 7955 and 7956 chips. In addition to all the features of the previous 7951 chip, these add AES.

  Hifn was initially a difficult company to deal with (threatening to sue us over our non-USA reverse engineering of their crypto unlock algorithm), but more recently they have been very helpful in providing boards and support.

• Hifn 6500
  This device is an asymmetric crypto unit. It has support for RSA, DSA, and DH algorithms, as well as other major big number functions. It also contains a very high performance random number generator. We have one device, full documentation, and sample code. As of OpenBSD 3.1, both the random number generator and big number unit are working.

• Hifn 7814/7851/7854
  This device is a packet processor and asymmetric crypto unit. It has support for RSA, DSA, and DH algorithms, as well as other major big number functions and also has a random number generator. Currently, only the big number engine and the random number generator are supported (no packet transforms).

• Broadcom BCM5801/BCM5802/BCM5805/BCM5820/BCM5821/BCM5822/5823/5825/5860/5861/5862 (or beta chip Bluesteelnet 5501/5601)
  Just after the OpenBSD 2.7 release, we succeeded at adding preliminary support for these early release parts provided to us by the vendor, specifically starting with the test chip 5501. These devices provide the highest performance symmetric cryptography we have seen.

  Bluesteelnet was bought by Broadcom and started making real parts. Their new BCM5805 is similar, except that they also add an asymmetric engine for running DSA, RSA, and other such algorithms. With approximate performance starting at more than four times as fast as the Hifn, hopefully this chip will become more common soon.

  The Broadcom/Bluesteelnet people have been great to deal with. They gave us complete documentation and sample code for their chips and a sufficient number of cards to test with.

  Post 2.8, this driver was also modified to generate random numbers on the BCM5805 and similar versions, and feed that data into the kernel entropy pool.

  Post 2.9, support was added for the BCM5820, which is mostly just a faster (64bit, higher clock speed) version of the BCM5805. Untested support for the BCM5821 was also added post 3.0.

  As of 3.1, the big num engine is supported, and RSA/DH/DSA operations can be accelerated.

  Support for the BCM5801, BCM5802, BCM5821 and BCM5822 was added before OpenBSD 3.2 (the untested BCM5821 support in 3.1 was broken because of some undocumented interrupt handling requirements).

  Partial support for BCM5823 was added for 3.4.

  Support for the BCM5825, BCM5860, BCM5861, and BCM5862 including support for AES with the BCM5823 or newer was added after 4.5.

• Securealink PCC-ISES
  The PCC-ISES is a new chipset from the Netherlands. We have received sample hardware and documentation, and work on a driver is in progress. At the moment, the driver is capable of feeding random numbers into the kernel entropy pool.

• SafeNet SafeXcel 1141/1741
  After 3.4 shipped, support was for added for these two chips (found on various SafeNet crypto cards. Supports DES, Triple-DES, AES, MD5, and SHA-1 symmetric crypto operations, RNG, public key operations, and full IPsec packet processing.

• SafeNet SafeXcel 1840
  We have received documentation and sample hardware for the SafeNet 1840 crypto chip. Work to support at least the RNG and symmetric cryptography of these devices has started.

• SafeNet SafeXcel 2141
  We have received documentation and sample hardware for the SafeNet 2141 crypto chip. Work to support at least the symmetric cryptography of these devices has started.

• 3com 3cr990
  3com gave us a driver to support the ethernet component of this chipset, and based on that, we have written our own ethernet driver. This driver has now been integrated once we were able to get a free license on the microcode. Due to poor documentation and lack of cooperation (partly because of the high turnover rates at 3Com), the IPsec functions of the chip are not supported.... so this turned out to be a less than completely useful exercise.

• Intel IPsec card
  Much like Intel does for all their networking division components, and completely unlike most other vendors, Intel steadfastly refuses to provide us with documentation. We have talked to about five technical people who are involved in the development of those products. They all want us to have documentation. They commend us on what we have done. But their hands are tied by management who does not perceive a benefit to themselves for providing documentation. Forget about Intel. (If you want to buy gigabit ethernet hardware, we recommend anything else... for the same reason: most drivers we have for Intel networking hardware were written without documentation).

• Intel 82802AB/82802AC Firmware Hub RNG
  The 82802 FWH chip (found on i810, i820, i840, i850, and i860 motherboards) contains a random number generator (RNG). High-performance IPsec requires more random number entropy. As of April 10, 2000, we support the RNG. We will add support for other RNGs found on crypto chips.

• VIA C3 RNG
  The newer VIA C3 CPU contains a random number generator as an instruction. As of 3.3 this random number generator is used inside the kernel to feed the entropy pool.

• VIA C3 AES instructions
  VIA C3 CPUs with a step 8 or later Nehemiah core contains an AES implementation accessible via simple instructions. As of 3.4 the kernel supports them to be used in an IPsec context and exported by /dev/crypto. As of 3.5 performances have been greatly improved and OpenSSL now uses the new instruction directly when available without the need to enter the kernel, resulting in vastly improved speed (AES-128 measured at 780MByte/sec) for applications using OpenSSL to perform AES encryption.

• OpenSSL
  Years ago, we had a grand scheme to support crypto cards that can do RSA/DH/DSA automatically via OpenSSL calls. As of OpenBSD 3.2, that support works, and any card that is supported with such functionality will automatically use the hardware, including OpenSSH and httpd in SSL mode. No application changes are required.

如果有人愿意帮助编写驱动程序，请加入我们的行列。

寻找国际密码系统安全专家

当然，我们的项目需要人们来开发这些系统。 如果有非美国的密码学专家满足上述要求，愿意帮助我们开发嵌入 OpenBSD 的密码学系统，请联系我们。

进阶读物

OpenBSD 团队成员已经撰写了很多关于他们在 OpenBSD 的密码学系统方面所作改变的资料。这些文档的 postscript 格式可从下列地址获取。

• A Future-Adaptable Password Scheme.
  Usenix 1999, by Niels Provos, David Mazieres.
  paper and slides.

• Cryptography in OpenBSD: An Overview.
  Usenix 1999, by Theo de Raadt, Niklas Hallqvist, Artur Grabowski, Angelos D. Keromytis, Niels Provos.
  paper and slides.

• Implementing Internet Key Exchange (IKE).
  Usenix 2000, by Niklas Hallqvist and Angelos D. Keromytis.
  paper and slides.

• Encrypting Virtual Memory.
  Usenix Security 2000, Niels Provos.
  paper and slides.

• The Design of the OpenBSD Cryptographic Framework.
  Usenix 2003, by Angelos D. Keromytis, Jason L. Wright, and Theo de Raadt.
  paper.

• Cryptography As an Operating System Service: A Case Study.
  ACM Transactions on Computer Systems, February 2006, by Angelos D. Keromytis, Jason L. Wright, and Theo de Raadt.
  paper.