Une collision sha256 est-elle possible ? [Hash, Math, Blog] by peneinc

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fr · @peneinc · Nov 17 '18

$0.02

Une collision sha256 est-elle possible ? [Hash, Math, Blog]

https://keyword-hero.com/wp-content/uploads/2017/05/sha256-1.png

Oui, c'est possible. Mais la(les) question(s) devrais être :

- Quand ?
- Avec quel conditions ?

Avant d'y répondre, il faut savoir que les calcules que je vais faire plus bas, sont des estimations. Une collisions arrive de façon "aléatoire" et non prévisible. La réponse a la question "Quand ?" seras le nombre d'années MAXIMALES pour tomber sur une collisions. ( En fonction des paramètres pris en compte  ). La réponse vas donc varier en fonction des scénarios dans la quel le calcule est effectué.

Un Sha256 retourne une valeur constitué  de lettres majuscule, minuscules et de chiffre de 0 à 9. Il y à donc ~64^36 combinaisons possible. Pour que ce nombre soit plus parlant ... 

Sha256 :  105 312 291 668 557 186 697 918 027 683 670 432 318 895 095 400 549 111 254 310 977 536

Il vas donc maintenant être question  : Avec quel conditions ?

Et pour ça on vas regarder la force de calcule du Bitcoin. Le hasrate TOTAL du bitcoin a cette heure si est de : 
42 672 924 Trillion/Hash/s.

Avec cette force de calcule, et si elle n'évolue pas avec le temps. ( Oui car sur 1 ans la force de calcule et les technologie évolue beaucoup. Et comme on vas parler en nombre d'années avec plus de 30 chiffres.. ça pourrais tout changer ! ).  Il nous faudrait environs : ...

78 256 434 036 333 969 729 345 924 683 144 455 907 Années pour générer la totalité des combinaisons du sha256 et donc de tomber sur notre première collision, suivis uniquement de collision car on déjà tout.. Enfin..

Ps : Si vous voulez refaire le calcule avec des scénario différent, j'ai fait une petite calculatrice en javascript :)

var hashPerSeconds = 42672924000000000000;
var sha256Posibility = 105312291668557186697918027683670432318895095400549111254310977536;
var secondsPerYear = 31536000;
var hashPerYear = hashPerSeconds * secondsPerYear;
var result = sha256Posibility / hashPerYear;
console.log( result );
 

Liens utiles : 
https://defuse.ca/big-number-calculator.htm
https://www.blockchain.com/fr/charts/hash-rate
https://en.bitcoin.it/wiki/SHA-256
https://fr.wikipedia.org/wiki/SHA-2

👍 iptrucs, fyrstikken, qurator-tier-0, kaliangel, peneinc, bobflix

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@bobflix · Nov 18 '18

intéressant, mais pour quelle raison calcule,au lieu de calcul ?
en informatique rien n'est impossible !

👍 peneinc

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@peneinc · Nov 21 '18

42 😰

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@iptrucs · Nov 18 '18

Article intéressant, tu aurais pu préciser que SHA256 signifie Secure Hash Algorithm sur 256 bits codés en hexadécimal sur 64 caractères (64x4=256). Cela permet notamment de calculer les fameuses « chains » des blockchains.

👍 peneinc

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@steemitboard · Nov 17 '18

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@steemitboard · Mar 3 '19

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@steemitboard · Mar 5 '20

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