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4 votes
Accepted

How to make a document truly read only

Cryptography studies properties of information. Information, at least in discrete form (a sequence of bits) can inherently be duplicated. Inasmuch as a document conveys meaning, it can be expressed as ...
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3 votes
Accepted

Activation keys and asymmetric encryption

You can not compress an RSA signature much below the private modulus size. All methods that I know double the cost of either signing or verifying for each extra bit trimmed, after the first one or two ...
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  • 122k
1 vote

How does PUF hardware help in software activation?

You're right about hardware activation devices for desktop applications. Dangling dongles outa your printer port is quite legacy. New applications tend to use some form of on-line activation system. ...
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  • 13.8k
1 vote

Are there secure public domain crypto or license management algos? Or are just commercial algos "commercial-grade"?

All good cryptographic algorithms are public domain. "Commercial" cryptographic algorithms are almost always snake oil. Now, there is a difference between the algorithm and an implementation of an ...
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  • 19.2k
1 vote
Accepted

AES-CBC pre-determined IV vs. null IV

There's no practical difference between zero IV and any other constant IV here. With some older ciphers that have a small enough keyspace (or weaknesses that allow reducing it) you could have a ...
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  • 31.2k
1 vote

One-time token to decrypt a local file

In a practical sense you could use a HSM for this where an asymmetric (RSA) private key is stored. In at least some HSM's it is possible to set a maximum usage count. You could program a similar usage ...
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  • 84.7k

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