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Security professional with many years of experience with the practical application of cryptographic algorithms and protocols. I'm helping with the design of protocols and API's within international standardization bodies. Lead developer of a common criteria certified product. Over 30 years of general experience with computers.

On crypto I mainly answer less mathematically inclined questions, leaving security proofs to the theoretical cryptographers and analysts.


Nov
23
comment Is salt bring more security for digital signature!
A salt is commonly used for key derivation functions, not for signature generation functions. If you think otherwise, please provide us information about the signature algorithm.
Nov
22
comment PHP secure random number generator
I think my alteration of the above comment crossed the one you were writing, I think the Java class containing nextInt(int) should be sufficiently "pseudo code" to be used. Obviously it misses the calculation of the range and $min + but I presume that doesn't pose a problem.
Nov
22
comment PHP secure random number generator
No, I meant that floating point numbers shouldn't be used at all, you get into trouble with rounding errors and such. Those may slightly alter the distribution, and slight errors in crypto almost always end up in less slight attacks. Take a look at for instance the Java Random class on how to do this using integers.
Nov
22
comment PHP secure random number generator
One thing that I've learned is to avoid floating point numbers at all cost. This can and should be solved using integer (discrete) math.
Nov
21
revised Hash collision using the leading 40-bits of SHA-1
added 92 characters in body; edited title
Nov
21
comment Hash collision using the leading 40-bits of SHA-1
@user1813580 A quick test confirms this.
Nov
21
comment Hash collision using the leading 40-bits of SHA-1
will find a collision -> won't find a collision?
Nov
21
comment Encryption of big files in Java with AES/GCM
@alejo I started to doubt myself and have looked up the requirements from NIST SP 800-38D and changed my answer accordingly. If unsure, look up the standard document.
Nov
21
revised Encryption of big files in Java with AES/GCM
deleted 97 characters in body
Nov
20
comment Difference between signing with SHA256 vs. signing with RSA-SHA256
This question appears to be off-topic because it is about a specific API
Nov
20
comment AES - Encrypting multiple blocks of files
If you prefix something it becomes larger? If the maximum size of the encrypted blocks can be somewhat larger than the plaintext you can just use CBC + padding or CTR and prefix the IV.
Nov
20
comment Should I study advanced abstract algebra and more than elementary number theory to pursue a career in cryptography?
I would gobble up any maths on discrete numbers that you can find + statistics. Without that background it is hard to succeed as a cryptographer. A math study will provide a better background than computer science in that regard. Yes, even most cryptographers may not understand EC fully, it would be beneficial if you can read safecurves.cr.yp.to without blinking too much. This advice was brought to you by somebody that stumbled into crypto slightly late and didn't gobble up that much math in the process.
Nov
20
revised Availability of a simple limited PRNG algorithm
edited title
Nov
19
revised Encryption of big files in Java with AES/GCM
added 75 characters in body
Nov
19
revised Encryption of big files in Java with AES/GCM
added 75 characters in body
Nov
19
comment Encryption of big files in Java with AES/GCM
@archie Thanks for the warning. Note that you can always place the BC provider on top of the list of providers and have that take over, or make the provider configurable. I'll take another look at GCM as in Java 8, also because of a few updates regarding bugs with CipherInputStream. This is brand new functionality and is still a bit in movement.
Nov
19
comment AES - Encrypting multiple blocks of files
Explained this in the answer instead of a comment, I apologize if I unnecessarily complicated things, but otherwise the encryption of files is completely standard.
Nov
19
revised AES - Encrypting multiple blocks of files
added 191 characters in body
Nov
19
comment Should I use a key store to keep my symmetric keys
And remember, an AES key consists of bits, not characters. In other words, it is not a String.
Nov
19
comment Should I use a key store to keep my symmetric keys
The key store has one big problem with it, it needs a password to be secure. The question then becomes where to store the password. In the end you require something that is trusted and - according to your description - unique per customer. Key management is however too big a topic to topple here, it all depends on your system.