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authorRaimo Niskanen <[email protected]>2017-09-19 15:33:53 +0200
committerRaimo Niskanen <[email protected]>2017-09-24 18:35:01 +0200
commit29222f06f38e321e5a2ac8dae67ced92b6544bde (patch)
treea61c429b229eedebde9216410ba65a6b58e82526 /lib/crypto/doc
parent32e3459206940ebfe6364f6936d7feb43bd27704 (diff)
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Document crypto rand cache
Diffstat (limited to 'lib/crypto/doc')
-rw-r--r--lib/crypto/doc/src/crypto.xml111
1 files changed, 109 insertions, 2 deletions
diff --git a/lib/crypto/doc/src/crypto.xml b/lib/crypto/doc/src/crypto.xml
index 89ef529c5d..5afab632cd 100644
--- a/lib/crypto/doc/src/crypto.xml
+++ b/lib/crypto/doc/src/crypto.xml
@@ -739,9 +739,16 @@
<seealso marker="stdlib:rand">random number generation</seealso>,
in order to generate cryptographically strong random numbers
(based on OpenSSL's <c>BN_rand_range</c>),
- and saves it on process dictionary before returning it as well.
+ and saves it in the process dictionary before returning it as well.
See also
- <seealso marker="stdlib:rand#seed-1">rand:seed/1</seealso>.
+ <seealso marker="stdlib:rand#seed-1">rand:seed/1</seealso> and
+ <seealso marker="#rand_seed_s-0">rand_seed_s/0</seealso>.
+ </p>
+ <p>
+ When using the state object from this function the
+ <seealso marker="stdlib:rand">rand</seealso> functions using it
+ may throw exception <c>low_entropy</c> in case the random generator
+ failed due to lack of secure "randomness".
</p>
<p><em>Example</em></p>
<pre>
@@ -763,6 +770,106 @@ _FloatValue = rand:uniform(). % [0.0; 1.0[</pre>
See also
<seealso marker="stdlib:rand#seed_s-1">rand:seed_s/1</seealso>.
</p>
+ <p>
+ When using the state object from this function the
+ <seealso marker="stdlib:rand">rand</seealso> functions using it
+ may throw exception <c>low_entropy</c> in case the random generator
+ failed due to lack of secure "randomness".
+ </p>
+ <note>
+ <p>
+ The state returned from this function can not be used
+ to get a reproducable random sequence as from
+ the other
+ <seealso marker="stdlib:rand">rand</seealso>
+ functions,
+ since reproducability does not match cryptographically safe.
+ </p>
+ <p>
+ The only supported usage is to generate one distinct
+ random sequence from this start state.
+ </p>
+ </note>
+ </desc>
+ </func>
+
+ <func>
+ <name>rand_seed_alg(Alg) -> rand:state()</name>
+ <fsummary>Strong random number generation plugin state</fsummary>
+ <type>
+ <v>Alg = crypto | crypto_cache</v>
+ </type>
+ <desc>
+ <p>
+ Creates state object for
+ <seealso marker="stdlib:rand">random number generation</seealso>,
+ in order to generate cryptographically strong random numbers.
+ See also
+ <seealso marker="stdlib:rand#seed-1">rand:seed/1</seealso> and
+ <seealso marker="#rand_seed_alg_s-1">rand_seed_alg_s/1</seealso>.
+ </p>
+ <p>
+ When using the state object from this function the
+ <seealso marker="stdlib:rand">rand</seealso> functions using it
+ may throw exception <c>low_entropy</c> in case the random generator
+ failed due to lack of secure "randomness".
+ </p>
+ <p><em>Example</em></p>
+ <pre>
+_ = crypto:rand_seed_alg(crypto_cache),
+_IntegerValue = rand:uniform(42), % [1; 42]
+_FloatValue = rand:uniform(). % [0.0; 1.0[</pre>
+ </desc>
+ </func>
+
+ <func>
+ <name>rand_seed_alg_s(Alg) -> rand:state()</name>
+ <fsummary>Strong random number generation plugin state</fsummary>
+ <type>
+ <v>Alg = crypto | crypto_cache</v>
+ </type>
+ <desc>
+ <p>
+ Creates state object for
+ <seealso marker="stdlib:rand">random number generation</seealso>,
+ in order to generate cryptographically strongly random numbers.
+ See also
+ <seealso marker="stdlib:rand#seed_s-1">rand:seed_s/1</seealso>.
+ </p>
+ <p>
+ If <c>Alg</c> is <c>crypto</c> this function behaves exactly like
+ <seealso marker="#rand_seed_s-0">rand_seed_s/0</seealso>.
+ </p>
+ <p>
+ If <c>Alg</c> is <c>crypto_cache</c> this function
+ fetches random data with OpenSSL's <c>RAND_bytes</c>
+ and caches it for speed using an internal word size
+ of 56 bits that makes calculations fast on 64 bit machines.
+ </p>
+ <p>
+ When using the state object from this function the
+ <seealso marker="stdlib:rand">rand</seealso> functions using it
+ may throw exception <c>low_entropy</c> in case the random generator
+ failed due to lack of secure "randomness".
+ </p>
+ <note>
+ <p>
+ The state returned from this function can not be used
+ to get a reproducable random sequence as from
+ the other
+ <seealso marker="stdlib:rand">rand</seealso>
+ functions,
+ since reproducability does not match cryptographically safe.
+ </p>
+ <p>
+ In fact since random data is cached some numbers may
+ get reproduced if you try, but this is unpredictable.
+ </p>
+ <p>
+ The only supported usage is to generate one distinct
+ random sequence from this start state.
+ </p>
+ </note>
</desc>
</func>