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Jan
7
comment Do I have to transfer the private key to digitally sign a remote document?
If anything is preventing you from transmitting the unsigned pdf back to the client for signing, I am afraid the problem is with your requirements. You will either need some basic pdf parser client side, or you will have to let the server sign the document using a certificate that is not issued for the client. You can't have it both ways.
Dec
30
comment Do I have to transfer the private key to digitally sign a remote document?
Transfer the preliminary pdf to the client, let the client sign it and upload it back to the server. Alternatively, let the server sign it with a key corresponding to a certificate that belongs to the service rather than the user.
Dec
29
comment Do I have to transfer the private key to digitally sign a remote document?
What exactly does "DSC" mean in this context?
Dec
26
comment Prime Numbers in Discrete Log
You have chosen the tag "dsa", but there is no mention of digital signatures in your question. Do you need primes for Diffie-Hellman or for a signature scheme?
Dec
26
comment Which Block cipher mode should I use?
Define "secure".
Dec
15
comment What is difference between PRG, PRF, and PRP
Well, a poly-time observer has a relatively realistically good shot at distinguishing a few TB of a AES-CTR stream from a HMAC-MD5-stream, but not at distinguishing AES with a random key from a random permutation.
Nov
17
comment Key generation in Digital Signature Algorithm
The exact algorithm for generating the primes is specified in the DSS NIST FIPS 186-4 nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.186-4.pdf
Nov
15
comment Why we can't implement AES 512 key size?
"since AES-128 is safe enough for anything foreseeable" ...except when the cryptosystem is re-keying sufficiently frequently for collisions in the key space to become a concern.
Oct
3
comment What does OIW stand for
books.google.se/…
Oct
3
comment What does OIW stand for
Open System Implementors Workshop alvestrand.no/objectid/1.3.14.html
Sep
23
comment Is it possible to find out whether a number is greater than another number without knowing the numbers?
Do you need to compare each number in a pair only once, or multiple times?
Sep
22
comment Is it possible to hand-negotiate an SSL/TLS session?
No, it is not feasible or even theoretically possible to connect to a server on 443 and type yourself through an entire SSL handshake.
Sep
15
comment What is the technical name for a public key container in DER format?
If it's not a plain PKCS#1 RSAPublicKey, it is probably a SubjectPublicKeyInfo from PKIX/X.509
Sep
15
comment What is the technical name for a public key container in DER format?
Well, you don't have to take my word for it. All you have to do is to implement a Base64 decoder, an ASN.1 parser, a DER parser and see for yourself, just like I did. :)
Sep
15
comment What is the technical name for a public key container in DER format?
The format is PKCS#1 with PEM encoding. Your question is however off topic here.
Sep
15
comment Why would an RSA library tell me that the public key must be at least 512 bits in size?
Obviously, you can't use a 512 bit RSA key for generating sha512withRSAEncryption signatures. The restriction on key size might have to with more than just best practices.
Sep
3
comment Are SSL/TLS used for maintaining data confidentiality?
Please read the answer again. Data as a whole might not necessarily be confidential, just because it is encrypted. The hash functions are used for the message authentication codes and (in TLS 1.2 and up) for the PRF that is used e.g. for deriving bulk encryption keys. The description in the other answer crypto.stackexchange.com/a/18936/1564 is generally correct in this respect.
Aug
22
comment Why does DES use exactly 16 rounds?
@fgrieu You are probably correct.
Aug
12
comment Deterministic Rand function for Winternitz One Time Signatures
I need (at least) 256 bit outputs because the Winternitz OWF has a 256 bit output. I need (at least) a 256 bit key, because the risk of collisions in the leaf keys must nut exceed the risk of collisions in the message digest function. I need a 256 bit seed because the number of leafs is $2^{250}$ and the total number of independent leaf keys is $2^{256}$.
Aug
11
comment SHACAL in SHA-256
Yes, SHACAL-2 was e.g. selected as part of the NESSIE portfolio. However, it should be noted that some standard modes of operation don't have a 256-bit equivalent, such as GCM.