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1 | |
2 | Scatterlist Cryptographic API | |
3 | ||
4 | INTRODUCTION | |
5 | ||
6 | The Scatterlist Crypto API takes page vectors (scatterlists) as | |
7 | arguments, and works directly on pages. In some cases (e.g. ECB | |
8 | mode ciphers), this will allow for pages to be encrypted in-place | |
9 | with no copying. | |
10 | ||
11 | One of the initial goals of this design was to readily support IPsec, | |
12 | so that processing can be applied to paged skb's without the need | |
13 | for linearization. | |
14 | ||
15 | ||
16 | DETAILS | |
17 | ||
18 | At the lowest level are algorithms, which register dynamically with the | |
19 | API. | |
20 | ||
21 | 'Transforms' are user-instantiated objects, which maintain state, handle all | |
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22 | of the implementation logic (e.g. manipulating page vectors) and provide an |
23 | abstraction to the underlying algorithms. However, at the user | |
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24 | level they are very simple. |
25 | ||
26 | Conceptually, the API layering looks like this: | |
27 | ||
28 | [transform api] (user interface) | |
878b9014 | 29 | [transform ops] (per-type logic glue e.g. cipher.c, compress.c) |
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30 | [algorithm api] (for registering algorithms) |
31 | ||
32 | The idea is to make the user interface and algorithm registration API | |
33 | very simple, while hiding the core logic from both. Many good ideas | |
34 | from existing APIs such as Cryptoapi and Nettle have been adapted for this. | |
35 | ||
36 | The API currently supports three types of transforms: Ciphers, Digests and | |
37 | Compressors. The compression algorithms especially seem to be performing | |
38 | very well so far. | |
39 | ||
40 | Support for hardware crypto devices via an asynchronous interface is | |
41 | under development. | |
42 | ||
43 | Here's an example of how to use the API: | |
44 | ||
45 | #include <linux/crypto.h> | |
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46 | #include <linux/err.h> |
47 | #include <linux/scatterlist.h> | |
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48 | |
49 | struct scatterlist sg[2]; | |
50 | char result[128]; | |
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51 | struct crypto_hash *tfm; |
52 | struct hash_desc desc; | |
1da177e4 | 53 | |
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54 | tfm = crypto_alloc_hash("md5", 0, CRYPTO_ALG_ASYNC); |
55 | if (IS_ERR(tfm)) | |
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56 | fail(); |
57 | ||
58 | /* ... set up the scatterlists ... */ | |
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59 | |
60 | desc.tfm = tfm; | |
61 | desc.flags = 0; | |
1da177e4 | 62 | |
58e40308 | 63 | if (crypto_hash_digest(&desc, sg, 2, result)) |
878b9014 | 64 | fail(); |
1da177e4 | 65 | |
878b9014 | 66 | crypto_free_hash(tfm); |
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67 | |
68 | ||
69 | Many real examples are available in the regression test module (tcrypt.c). | |
70 | ||
71 | ||
72 | CONFIGURATION NOTES | |
73 | ||
74 | As Triple DES is part of the DES module, for those using modular builds, | |
75 | add the following line to /etc/modprobe.conf: | |
76 | ||
77 | alias des3_ede des | |
78 | ||
79 | The Null algorithms reside in the crypto_null module, so these lines | |
80 | should also be added: | |
81 | ||
82 | alias cipher_null crypto_null | |
83 | alias digest_null crypto_null | |
84 | alias compress_null crypto_null | |
85 | ||
86 | The SHA384 algorithm shares code within the SHA512 module, so you'll | |
87 | also need: | |
88 | alias sha384 sha512 | |
89 | ||
90 | ||
91 | DEVELOPER NOTES | |
92 | ||
93 | Transforms may only be allocated in user context, and cryptographic | |
94 | methods may only be called from softirq and user contexts. | |
95 | ||
96 | When using the API for ciphers, performance will be optimal if each | |
97 | scatterlist contains data which is a multiple of the cipher's block | |
98 | size (typically 8 bytes). This prevents having to do any copying | |
99 | across non-aligned page fragment boundaries. | |
100 | ||
101 | ||
102 | ADDING NEW ALGORITHMS | |
103 | ||
104 | When submitting a new algorithm for inclusion, a mandatory requirement | |
105 | is that at least a few test vectors from known sources (preferably | |
106 | standards) be included. | |
107 | ||
108 | Converting existing well known code is preferred, as it is more likely | |
109 | to have been reviewed and widely tested. If submitting code from LGPL | |
110 | sources, please consider changing the license to GPL (see section 3 of | |
111 | the LGPL). | |
112 | ||
113 | Algorithms submitted must also be generally patent-free (e.g. IDEA | |
114 | will not be included in the mainline until around 2011), and be based | |
115 | on a recognized standard and/or have been subjected to appropriate | |
116 | peer review. | |
117 | ||
118 | Also check for any RFCs which may relate to the use of specific algorithms, | |
119 | as well as general application notes such as RFC2451 ("The ESP CBC-Mode | |
120 | Cipher Algorithms"). | |
121 | ||
122 | It's a good idea to avoid using lots of macros and use inlined functions | |
123 | instead, as gcc does a good job with inlining, while excessive use of | |
124 | macros can cause compilation problems on some platforms. | |
125 | ||
126 | Also check the TODO list at the web site listed below to see what people | |
127 | might already be working on. | |
128 | ||
129 | ||
130 | BUGS | |
131 | ||
132 | Send bug reports to: | |
878b9014 | 133 | Herbert Xu <herbert@gondor.apana.org.au> |
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134 | Cc: David S. Miller <davem@redhat.com> |
135 | ||
136 | ||
137 | FURTHER INFORMATION | |
138 | ||
139 | For further patches and various updates, including the current TODO | |
140 | list, see: | |
878b9014 | 141 | http://gondor.apana.org.au/~herbert/crypto/ |
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142 | |
143 | ||
144 | AUTHORS | |
145 | ||
146 | James Morris | |
147 | David S. Miller | |
878b9014 | 148 | Herbert Xu |
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149 | |
150 | ||
151 | CREDITS | |
152 | ||
153 | The following people provided invaluable feedback during the development | |
154 | of the API: | |
155 | ||
156 | Alexey Kuznetzov | |
157 | Rusty Russell | |
158 | Herbert Valerio Riedel | |
159 | Jeff Garzik | |
160 | Michael Richardson | |
161 | Andrew Morton | |
162 | Ingo Oeser | |
163 | Christoph Hellwig | |
164 | ||
165 | Portions of this API were derived from the following projects: | |
166 | ||
167 | Kerneli Cryptoapi (http://www.kerneli.org/) | |
168 | Alexander Kjeldaas | |
169 | Herbert Valerio Riedel | |
170 | Kyle McMartin | |
171 | Jean-Luc Cooke | |
172 | David Bryson | |
173 | Clemens Fruhwirth | |
174 | Tobias Ringstrom | |
175 | Harald Welte | |
176 | ||
177 | and; | |
178 | ||
179 | Nettle (http://www.lysator.liu.se/~nisse/nettle/) | |
be2a608b | 180 | Niels Möller |
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181 | |
182 | Original developers of the crypto algorithms: | |
183 | ||
184 | Dana L. How (DES) | |
185 | Andrew Tridgell and Steve French (MD4) | |
186 | Colin Plumb (MD5) | |
187 | Steve Reid (SHA1) | |
188 | Jean-Luc Cooke (SHA256, SHA384, SHA512) | |
189 | Kazunori Miyazawa / USAGI (HMAC) | |
190 | Matthew Skala (Twofish) | |
191 | Dag Arne Osvik (Serpent) | |
192 | Brian Gladman (AES) | |
193 | Kartikey Mahendra Bhatt (CAST6) | |
194 | Jon Oberheide (ARC4) | |
195 | Jouni Malinen (Michael MIC) | |
dc2e2f33 | 196 | NTT(Nippon Telegraph and Telephone Corporation) (Camellia) |
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197 | |
198 | SHA1 algorithm contributors: | |
199 | Jean-Francois Dive | |
200 | ||
201 | DES algorithm contributors: | |
202 | Raimar Falke | |
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203 | Gisle Sælensminde |
204 | Niels Möller | |
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205 | |
206 | Blowfish algorithm contributors: | |
207 | Herbert Valerio Riedel | |
208 | Kyle McMartin | |
209 | ||
210 | Twofish algorithm contributors: | |
211 | Werner Koch | |
212 | Marc Mutz | |
213 | ||
214 | SHA256/384/512 algorithm contributors: | |
215 | Andrew McDonald | |
216 | Kyle McMartin | |
217 | Herbert Valerio Riedel | |
218 | ||
219 | AES algorithm contributors: | |
220 | Alexander Kjeldaas | |
221 | Herbert Valerio Riedel | |
222 | Kyle McMartin | |
223 | Adam J. Richter | |
224 | Fruhwirth Clemens (i586) | |
225 | Linus Torvalds (i586) | |
226 | ||
227 | CAST5 algorithm contributors: | |
228 | Kartikey Mahendra Bhatt (original developers unknown, FSF copyright). | |
229 | ||
230 | TEA/XTEA algorithm contributors: | |
231 | Aaron Grothe | |
fb4f10ed | 232 | Michael Ringe |
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233 | |
234 | Khazad algorithm contributors: | |
235 | Aaron Grothe | |
236 | ||
237 | Whirlpool algorithm contributors: | |
238 | Aaron Grothe | |
239 | Jean-Luc Cooke | |
240 | ||
241 | Anubis algorithm contributors: | |
242 | Aaron Grothe | |
243 | ||
244 | Tiger algorithm contributors: | |
245 | Aaron Grothe | |
246 | ||
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247 | VIA PadLock contributors: |
248 | Michal Ludvig | |
249 | ||
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250 | Camellia algorithm contributors: |
251 | NTT(Nippon Telegraph and Telephone Corporation) (Camellia) | |
252 | ||
1da177e4 LT |
253 | Generic scatterwalk code by Adam J. Richter <adam@yggdrasil.com> |
254 | ||
255 | Please send any credits updates or corrections to: | |
878b9014 | 256 | Herbert Xu <herbert@gondor.apana.org.au> |
1da177e4 | 257 |