اطلب شرح مفصل عن Md5

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شرح : طريقة من أحدى الطرق لحماية برامج الشبكات, شرح مفصل وبسيط عن Md5

طريقه تشفير البيانات النصيه عن طريق مكتبه MD5, من أقوى مكتبات التشفير

تحياتي...

إضافة:

http://en.wikipedia.org/wiki/MD5

السلام عليكــم ورحمـة الله وبركاتــه ،،

لا اعرف كيف اشكركم لكن اقول

عسى الله ان يجزى الشباب الذين ردوا علي كل خير وأن يجعل جزاءهم جنة الفردوس هو ووالديهم امين امين امين

وان ييسر الله امرهم في كل شيء وان يفرج عنهم كل كرب امين امين امين

شكرا

طريقة MD5 لحماية كلمات السر تم كسرها وأصبح من الممكن إيجاد نصوص تتطابق في الـ MD5 الخاص بها مما يعني أنها لم تعد آمنة ويجب التوقف عن استخدامها واستخدام SHA بدلا منها أو استخدام طريقة salt معها

انظر الرابط التالي :

http://en.wikipedia.org/wiki/MD5

اقتباس

Vulnerability

In 1995, collisions were found in the compression function of MD5, and Hans Dobbertin wrote in the RSA Laboratories technical newsletter, "The presented attack does not yet threaten practical applications of MD5, but it comes rather close ... in the future MD5 should no longer be implemented...where a collision-resistant hash function is required."^[13]

In 2005, researchers were able to create pairs of PostScript documents^[14] and X.509 certificates^[15] with the same hash. Later that year, MD5's designer Ron Rivest wrote, "md5 and sha1 are both clearly broken (in terms of collision-resistance),"^[16] and RSA Laboratories wrote that "[n]ext-generation products will need to move to new algorithms."^[17]

On December 30, 2008, a group of researchers announced at the 25th Chaos Communication Congress how they had used MD5 collisions to create an intermediate certificate authority certificate which appeared to be legitimate when checked via its MD5 hash.^[5] The researchers used a cluster of Sony Playstation 3s at the EPFL in Lausanne, Switzerland^[18] to change a normal SSL certificate issued by RapidSSL into a working CA certificate for that issuer, which could then be used to create other certificates that would appear to be legitimate and issued by RapidSSL. VeriSign, the issuers of RapidSSL certificates, said they stopped issuing new certificates using MD5 as their checksum algorithm for RapidSSL once the vulnerability was announced.^[19] Although Verisign declined to revoke existing certificates signed using MD5, their response was considered adequate by the authors of the exploit (Alexander Sotirov, Marc Stevens, Jacob Appelbaum, Arjen Lenstra, David Molnar, Dag Arne Osvik, and Benne de Weger).^[5] Bruce Schneier wrote of the attack that "[w]e already knew that MD5 is a broken hash function" and that "no one should be using MD5 anymore."^[20] The SSL researchers wrote, "Our desired impact is that Certification Authorities will stop using MD5 in issuing new certificates. We also hope that use of MD5 in other applications will be reconsidered as well."^[5]

Because MD5 makes only one pass over the data, if two prefixes with the same hash can be constructed, a common suffix can be added to both to make the collision more likely to be accepted as valid data by the application using it. Furthermore, current collision-finding techniques allow to specify an arbitrary prefix: an attacker can create two colliding files that both begin with the same content. All the attacker needs to generate two colliding files is a template file with a 128-byte block of data aligned on a 64-byte boundary that can be changed freely by the collision-finding algorithm.

Recently, a number of projects have created MD5 rainbow tables which are easily accessible online, and can be used to reverse many MD5 hashes into strings that collide with the original input, usually for the purposes of password cracking. However, if passwords are combined with a salt before the MD5 digest is generated, rainbow tables become much less useful.

The use of MD5 in some websites' URLs means that Google can also sometimes function as a limited tool for reverse lookup of MD5 hashes.^[21] This technique is also rendered ineffective by the use of a salt.

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