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107 votes
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How come Public key cryptography wasn't discovered earlier?

If you read about Merkle's experience with bringing the subject to the mainstream, you might be surprised. His professor rejected his initial proposal and show little interest in any further ...
Ella Rose's user avatar
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71 votes

Soft question: Examples where lack of mathematical rigour cause security breaches?

The SSH protocol has a complicated record format with an encrypted message length, variable padding, encrypt-and-MAC, etc. This complicated system, which was designed without any formal analysis ...
Squeamish Ossifrage's user avatar
53 votes

Have any cryptographic breaks been executed in the real world since World War II?

One example that immediately comes to mind is the attack on WEP, which is based on an unknown (to the designers at the time) related key attack on RC4 that lead to a key recovery. It needs to be a ...
poncho's user avatar
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34 votes

How come Public key cryptography wasn't discovered earlier?

I guess the discovery of public key crypto was not earlier due to three combined factors: before (digital) computers, public key cryptography was impossible difficult to implement, and things that ...
fgrieu's user avatar
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33 votes
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Did a certain cryptography method get abandoned due to security flaws in the past?

You could be thinking about the Merkle-Hellman knapsack cryptosystem. It was invented in 1978 and everything seemed well and good until it was completely broken six years later in 1984 by Shamir - it ...
Thomas's user avatar
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33 votes
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Examples of modern, widely used ciphers that suddenly fell?

This question is quite broad by specifying a sudden fall to cryptanalysis and therefore my answer might not be as complete as you wish it to be. If by "become practically attackable, or close enough ...
Biv's user avatar
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29 votes

Have any cryptographic breaks been executed in the real world since World War II?

An example is GSM voice encryption using A5/1, used in Europe and USA on the voice channel of the radio link of cellphones before 3G. While with a good algorithm the 80-bit key size of A5/1 would be a ...
fgrieu's user avatar
  • 134k
28 votes

Have any cryptographic breaks been executed in the real world since World War II?

The DVD Content Scramble System. It needs to be a true cryptographic break, stemming from mathematical cryptanalysis Although the cipher is intrinsically weak, at only 40 bits, brute-forcing still ...
Mark's user avatar
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25 votes
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Why did Histiaeus tattoo his slave's head?

Exact motives will remain unknown, since we only have Herodotus's word for the whole story, and he doesn't say. However, we can imagine a plausible reason: the whole ordeal provides some level of ...
Thomas Pornin's user avatar
20 votes
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What was the first hash and what problem was it supposed to solve?

Knuth, TAOCP, Vol. 3, 6.4 states (on non cryptographic hashing): "The idea of hashing appears to have been originated by H. P. Luhn, who wrote an internal IBM memorandum in January 1953 that ...
kodlu's user avatar
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20 votes
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Have any cryptographic breaks been executed in the real world since World War II?

I'm no cryptographer, but I think the Flame malware matches your description. It's an extremely sophisticated tool for cyber espionage discovered in 2012. Experts believe it was developed by the US ...
Fabio says Reinstate Monica's user avatar
19 votes

Purpose of DES parity bits

Parity of DES key bytes was introduced on request of US authorities during the design of DES in the late 1970s: it mitigates the risk of accidental key alteration; in particular, any all-zeros or all-...
fgrieu's user avatar
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19 votes
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Purpose of DES parity bits

They are there to check if the key was indeed correctly retrieved. It could for instance be that the key is a result of key decryption or key agreement. In that case, or simply during transmission, ...
Maarten Bodewes's user avatar
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19 votes

Did a certain cryptography method get abandoned due to security flaws in the past?

This is a shot in the dark, but could you be thinking of the Needham-Schroeder protocol? It was published in 1978 [1], and an attack was published as much as 18 years later, in 1996 [2]. It is not an ...
Malte Skoruppa's user avatar
18 votes

Did a certain cryptography method get abandoned due to security flaws in the past?

DES has not been mentioned in the previous two answers. Although it was known to be quite weak from very early on it was widely used for a couple of decades at least, until newer algorithms (3DES, AES,...
otus's user avatar
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18 votes

Soft question: Examples where lack of mathematical rigour cause security breaches?

When choosing curves for use in elliptic curve cryptography, some have suggested using various classes of curves which avoid certain "bad" properties which would make the system vulnerable to attack. ...
Dave's user avatar
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17 votes
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How were one-time pads and keys historically generated?

Your interesting questions deserve to be answered more thoroughly, but here goes: According to a highly classified document written in 1947 and finally declassified in 2013, the Germans started using ...
Patriot's user avatar
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17 votes
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Is there any famous protocol that were proven secure but whose proof was wrong and lead to real world attacks?

One example is OCB2; Efficient Instantiations of Tweakable Blockciphers and Refinements to Modes OCB and PMAC by Rogaway. It is standardized in ISO/IEC 19772:2009. The author also provided a proof by ...
kelalaka's user avatar
  • 46k
16 votes

How come Public key cryptography wasn't discovered earlier?

I find the introduction to Hellman's 1979 Scientific American article titled "The Mathematics of Public-Key Cryptography" to be illuminating. According to the very authoritative Hellman, public key ...
Tobia Tesan's user avatar
15 votes
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Common Classical Ciphers

Cryptography as we know it today dates from the Renaissance, in a certain sense, in a mathematical sense. --Whitfield Diffie If you look at introductory cryptography texts, you will usually see some ...
Patriot's user avatar
  • 3,092
13 votes
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Where can I find a description of the SHA-0 hash algorithm?

The reference on SHA(-0) is FIPS 180 (archived scan) of 1993 May 11. The standard itself is referenced on the NIST website, but that links to another scan lacking page 1 and the one before, thus ...
fgrieu's user avatar
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13 votes
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Academic breach revealed too late

In 2004, Xiaoyun Wang's team first publicly reported collisions in MD5, and in 2007, Marc Stevens, Arjen Lenstra, and Benne de Weger reported a chosen-prefix collision attack on MD5. Around the same ...
Squeamish Ossifrage's user avatar
13 votes
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Who is the inventor of the OFB block cipher mode of operation?

It's difficult to be sure of the attribution here, but my best guess would be Carl M. Campbell Jr., from the (later renamed to Mastercard) Interbank Card Association. Soon after the DES was ...
Samuel Neves's user avatar
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12 votes
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Verbatim of early work on public-key cryptography?

My wishes largely came true! The GCHQ (briefly) published scans of [1] and [2], and another 1970 document: [1s]: James Ellis: The Possibility of Secure Non-Secret Digital Encryption [1.5s]: James ...
fgrieu's user avatar
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12 votes
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Is RSA inspired by Diffie Hellman?

Was RSA inspired by Diffe-Hellman, published the year before in 1976 Update I met Ron Rivest at MIT's LCS35 time capsule unveiling and asked him this question for you. The answer is yes. Original ...
Ella Rose's user avatar
  • 19.4k
12 votes

What motivated the creation of RSA and ECDH?

What I wonder is, what motivated the creation of RSA? Was it because they wanted to create something more secure than Diffie-Hellman? And if so, why is it more secure? The New Directions In ...
Ella Rose's user avatar
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11 votes
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Why was the Navajo code not broken by the Japanese in WWII?

Wrapping up my comment as an answer: Imagine you’re a Japanese cryptanalyst in the year 1944. There is no such thing yet called “television”, and you’re still decades away from a wordwide network ...
e-sushi's user avatar
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11 votes
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In the RSA DES challenges, how did the contestants know they had found the right key considering they weren't given any plaintext?

One can still access the challenge rules from the archive.org Each contest is based on a specified cipher. A brief piece of printable ASCII text (containing byte values in hexadecimal notation from ...
kelalaka's user avatar
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11 votes
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80-bit collision resistance because of 80-bit x87 registers?

Coprocessors are designed for improved performance in a certain case, and in the case of fixed-width mathematics, I do not believe you would see a performance increase. I am quite sure that 80-bits ...
b degnan's user avatar
  • 4,524
11 votes

Soft question: What are examples of beautiful proofs in cryptography?

Theorem. The ECB mode of a block cipher is distinguishable under chosen-plaintext attack with laughably high advantage. Proof.
Squeamish Ossifrage's user avatar

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