<?xml version="1.0" encoding="UTF-8"?><lom xmlns="http://ltsc.ieee.org/xsd/LOM" xmlns:lomfr="http://www.lom-fr.fr/xsd/LOMFR" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://ltsc.ieee.org/xsd/LOM http://www.lom-fr.fr/xsd/lomfrv1.0/std/lomfr.xsd">
<general>
<identifier>
<catalog>Canal-U_Ocms</catalog>
<entry>32979</entry>
</identifier>
<title><string language="fre"><![CDATA[5.3. Attacks against the CFS Scheme]]></string></title>
<language>ENG</language>
<description>
<string language="fre"><![CDATA[In this session, we will
have a look at the attacks against the CFS signature scheme. As for public-key
encryption, there are two kinds of attacks against signature schemes. First kind of attack is
key recovery attacks where an attacker tries to
recover the secret key from the knowledge of the public
key. These attacks are exactly the same as against the McEliece
cryptosystem that you have seen last week. The only difference is
the parameters. Here in the signature, we have a
small t and a large n but the algorithm remains the same. So, we won't go into
details in this session. The second kind of
attacks are forgery attacks. These attacks try to create
a valid document-signature pair that is a pair of
documented signature that a verifier will be able
to verify successfully. They are similar to message
attacks against McEliece but with one very simple
difference, that is, the attacker has a complete control on
the documents he wants to sign. Whereas in the McEliece
scheme, the attacker is given some ciphertexts and
tries to decrypt them. Depending on the version of
the CFS signature scheme, the forgery attack will
be slightly different. In the counter version of
CFS, the attacker will choose a document, pick a counter
i, compute the hash of the document and the counter
and try to decode this hash as an error of weight t. But,
be careful, hash is probably not decodable, only one out of t! is decodable. In the
complete decoding version, the attacker will choose a
document, compute this hash and try to decode it as an
error of weight t + ?. In both cases the attacker has to
solve an instance of syndrome decoding. And there are two main
algorithms to do this: Information Set Decoding or
Generalized Birthday Attack. The only difference is, as
we said, the attacker has a complete control on the document. So, instead of focusing
on a single document, the attacker can focus on
many documents at a time. Instead of choosing the
document and picking one counter, he can pick many counters
to obtain many different hash values, and among these hash
values, some will be decodable. In the complete decoding
version, the same thing, the attacker can choose many
documents and try to forge a signature for any of these documents.]]></string></description>
<keyword><string language="fre"><![CDATA[algèbre linéaire]]></string></keyword><keyword><string language="fre"><![CDATA[chiffrement à clé publique]]></string></keyword><keyword><string language="fre"><![CDATA[cryptage des données]]></string></keyword><keyword><string language="fre"><![CDATA[cryptographie]]></string></keyword><keyword><string language="fre"><![CDATA[code correcteur]]></string></keyword><keyword><string language="fre"><![CDATA[algorithmes]]></string></keyword><keyword><string language="fre"><![CDATA[CFS]]></string></keyword><keyword><string language="fre"><![CDATA[Courtois-Finiasz-Sendrier]]></string></keyword>
<lomfr:documentType>
<lomfr:source>LOMFRv1.0</lomfr:source>
<lomfr:value>image en mouvement</lomfr:value>
</lomfr:documentType>
</general><lifeCycle>
<contribute>
<role>
<source>LOMv1.0</source>
<value>author</value>
</role>
<entity><![CDATA[BEGIN:VCARD
VERSION:3.0
CLASS:PUBLIC
REV:2021-07-06 18:03:02
FN:Irene MARQUEZ-CORBELLA
N:MARQUEZ-CORBELLA;Irene;;;
URL;TYPE=work:https://www.canal-u.tv/auteurs/marquez_corbella_irene
ROLE:author
TZ:+0200
END:VCARD
]]></entity>
<date><dateTime>2015-05-05</dateTime></date>
</contribute>
<contribute>
<role>
<source>LOMv1.0</source>
<value>author</value>
</role>
<entity><![CDATA[BEGIN:VCARD
VERSION:3.0
CLASS:PUBLIC
REV:2021-07-06 18:03:02
FN:Nicolas SENDRIER
N:SENDRIER;Nicolas;;;
URL;TYPE=work:https://www.canal-u.tv/auteurs/sendrier_nicolas
ROLE:author
TZ:+0200
END:VCARD
]]></entity>
<date><dateTime>2015-05-05</dateTime></date>
</contribute>
<contribute>
<role>
<source>LOMv1.0</source>
<value>author</value>
</role>
<entity><![CDATA[BEGIN:VCARD
VERSION:3.0
CLASS:PUBLIC
REV:2021-07-06 18:03:02
FN:Matthieu FINIASZ
N:FINIASZ;Matthieu;;;
URL;TYPE=work:https://www.canal-u.tv/auteurs/finiasz_matthieu
ROLE:author
TZ:+0200
END:VCARD
]]></entity>
<date><dateTime>2015-05-05</dateTime></date>
</contribute>
</lifeCycle>
<metaMetadata>
<metadataSchema>LOMv1.0</metadataSchema>
<metadataSchema>LOMFRv1.0</metadataSchema>
</metaMetadata>
<technical>
<format>video/mp4</format>
<location><![CDATA[https://www.canal-u.tv/video/inria/5_3_attacks_against_the_cfs_scheme.32979]]></location>
<location><![CDATA[https://streaming-canal-u.fmsh.fr/vod/media/canalu/videos/fuscia/5.2.the.courtois.finiasz.sendrier.cfs.construction.copie._32979/c015im.w5.s3.mov]]></location>
<size>126347498</size>
<duration><duration>PT0H4M52S</duration></duration>
</technical>
<educational>
<learningResourceType>
<source>LOMv1.0</source>
<value>lecture</value>
</learningResourceType>
<context>
<source>LOMv1.0</source>
<value>master</value>
</context>
<context>
<source>LOMv1.0</source>
<value>doctorat</value>
</context>
</educational>
<rights>
<cost>
<source>LOMv1.0</source>
<value>no</value>
</cost>
<copyrightAndOtherRestrictions>
<source>LOMv1.0</source>
<value>no</value>
</copyrightAndOtherRestrictions>
<description>
<string language="fre"><![CDATA[Droits réservés à l'éditeur et aux auteurs. 
Ces ressources de cours sont, sauf mention contraire, diffusées sous Licence Creative Commons. L’utilisateur doit mentionner le nom de l’auteur, il peut exploiter l’œuvre sauf dans un contexte commercial et il ne peut apporter de modifications à l’œuvre originale.]]></string>
</description>
</rights>
<relation>
<kind>
<source>LOMv1.0</source>
<value>ispartof</value>
</kind>
<resource>
<identifier>
<catalog>URI</catalog>
<entry>https://www.canal-u.tv/producteurs/inria/cours_en_ligne/code_based_cryptography/5_other_cryptographic_constructions_relying_on_coding_theory</entry>
</identifier>
<description>
<string language="fre"><![CDATA[5: Other cryptographic constructions relying on coding theory]]></string>
</description>
</resource>
</relation>
<classification>
<purpose>
<source>LOMv1.0</source>
<value>discipline</value>
</purpose>
<taxonPath>
<source>
<string language="fre"><![CDATA[Universités Numériques Thématiques 2009 http://www.universites-numeriques.fr]]></string>
</source>
<taxon>
<id/>
<entry>
<string language="fre"/>
</entry>
</taxon>
</taxonPath>
</classification>
<classification>
<purpose>
<source>LOMv1.0</source>
<value>discipline</value>
</purpose>
<taxonPath>
<source>
<string language="fre">CDD 22e éd.</string>
<string language="eng">DDC 22nd ed.</string>
</source>
<taxon>
<id>518</id>
<entry>
<string language="fre"><![CDATA[Analyse numérique]]></string>
</entry>
</taxon>
</taxonPath>
<taxonPath>
<source>
<string language="fre">CDD 22e éd.</string>
<string language="eng">DDC 22nd ed.</string>
</source>
<taxon>
<id>003.54</id>
<entry>
<string language="fre"><![CDATA[Théorie de l'information]]></string>
</entry>
</taxon>
</taxonPath>
<taxonPath>
<source>
<string language="fre">CDD 22e éd.</string>
<string language="eng">DDC 22nd ed.</string>
</source>
<taxon>
<id>005.7</id>
<entry>
<string language="fre"><![CDATA[données dans les systèmes informatiques]]></string>
</entry>
</taxon>
</taxonPath>
<taxonPath>
<source>
<string language="fre">CDD 22e éd.</string>
<string language="eng">DDC 22nd ed.</string>
</source>
<taxon>
<id>652.8</id>
<entry>
<string language="fre"><![CDATA[cryptographie]]></string>
</entry>
</taxon>
</taxonPath>
<taxonPath>
<source>
<string language="fre">CDD 22e éd.</string>
<string language="eng">DDC 22nd ed.</string>
</source>
<taxon>
<id>510</id>
<entry>
<string language="fre"><![CDATA[Mathématiques]]></string>
</entry>
</taxon>
</taxonPath>
</classification> </lom>