Cryptography is the practice and study of logical means used to achieve information confidentiality, integrity and authenticity. It covers, among other things, encryption (making some data unreadable except for those who know a given secret element, called a key), data hashing (in particular for ...

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5answers
2k views

Why should I sign data that's already encrypted?

My question is about the difference between signing and encrypting. Why would you still sign something if you are already going to PKI encrypt it? Doesn't the PKI encryption inherently provide ...
0
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1answer
31 views

Forward Secrecy not supported with referenced browsers?

I am running a scan against one of our servers from the Qualys SSL tester site and it says that my server "does not support forward secrecy with the referenced browsers". What exactly does that mean? ...
3
votes
3answers
157 views

Is there any security gain / risk by adding additional padding (beyond what is required) when using AES-256 to encrypt very short strings?

I would like to encrypt some authentication tokens using AES 256 (not tied to this algorithm but it seems to be a reasonable choice). These messages are usually very short at 128-256 bits. I'm ...
0
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1answer
45 views

How are TLSv1.0 ciphers negotiated as TLSv1.2?

I'm a little confused about something I am reading in Bulletproof SSL. "TLS 1.2 is the only protocol that allows suites to define their PRFs. This means that for the suites defined before TLS 1.2 ...
0
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2answers
67 views

Encrypting using the private key in Identity-Based Cryptography

In normal asymmetric crpyto like RSA, if Alice encrypts something using her private key, Bob can decrypt it using Alice's public key. Is the same possible in Identity-Based Cryptography, where the ...
0
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2answers
49 views

ECDSA ciphers and forward secrecy question about key exchange

I have heard that with forward secrecy that the ECDSA ciphers generate different keys for "each session" because they are not dependent on the private key of the server. My question is how is "each ...
0
votes
0answers
26 views

How does Spideroak manage encryption keys

I'm trying to understand the following from SpiderOak's engineering page (sorry I'm on a mobile phone so have no access to formatting functions like quote blocks): "SpiderOak uses a nested series of ...
0
votes
1answer
70 views

What is the deal with Valicert SSL root certificates?

Does anyone know what the status of the "Valicert Class 2 Validation Authority" root certificate is or what's going on with Valicert in general? I've heard that that cert has been deprecated, no ...
1
vote
1answer
44 views

What is the purpose of “g” -> generator of the multiplicative group

I am currently beginning to studying the different security protocols and came across the SRP secure remote password protocol. I manage to understand the mathematic formulas behind it and the ...
1
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0answers
25 views

Key management for hosting applications

We're looking to host a number of client applications in our environment. Some of those will use crypto, e.g. for ssl or database encryption and obviously we'll need to manage keys for that. I am ...
1
vote
0answers
34 views

How is this SHA-1 hash generated? [closed]

If you get a disposable email from say guerrillamail.com, and then fill out the forgot my password page at dahorta.org/app/index.php/cliente/resgatar_senha, it emails you a link to reset your ...
4
votes
1answer
75 views

Is there a secure way to create and distribute Shamir Secrets?

This Shamir Secret sharing utility consumes the secret key, and then generates N keys that must be manually distributed to each person. This is probably fine for most low-security situations, but not ...
0
votes
1answer
62 views

Password Storage with Jasypt StrongPasswordEncryptor vs PBKDF2

We are currently working on authentication for a web application. For password storage, we're using Jasypt StrongPasswordEncryptor with SHA-256 and tens of thousands of iterations. Going into the ...
0
votes
1answer
153 views

4096 bit RSA encryption keys vs 2048

Where do 4096 bit RSA keys for SSL certs currently stand in terms of things like CA support, browser support, etc? In the overall scheme of things is the increased security worth the risk of 4096 bit ...
0
votes
2answers
60 views

Typical mistakes when implementing digital signatures?

I am looking for a list of typical mistakes someone can make when implementing digital signatures for a software. And of course why they are mistakes and how an attacker could take advantage of them. ...
1
vote
2answers
58 views

Do DES keys have to be random?

In stream cipher (namely the OTP ) . The pad which the plain text is Xored with has to be random to achieve perfect secrecy , or psudorandom to ensure semantic security Dose this apply to DES or ...
0
votes
3answers
122 views

Did the “Malicious SHA-1” technique enable the NSA to insert a backdoor into SHA-1?

SHA-1 was standardized by the NSA. It appears to be possible to choose the constants in such a way that collisions can be derived easily. Yet, it is not easily possible to discover that the constants ...
0
votes
0answers
52 views

Public/Private key validation

Suppose I have this scenario: User --> Inputs License Key --> I validate it --> If success, good, move onto main window. If not, prompt the user to reenter the license key. The license key will not ...
0
votes
0answers
29 views

Payment Application Integration - Encryption or HMAC

Doing an integration with an online payment provider. Payment provider will be making a web request to my server to provide some information about the basket content. On my end there's no payment ...
4
votes
2answers
96 views

How does an insecure RNG affect cryptography, and how do I measure the corresponding loss of security?

Suppose a given random number generator has poor entropy, and is compressible by any compression algorithm (zlib, bzip2, lzma, etc). Specifically the issues with this RNG are: Bad entropy Bad seed ...
2
votes
1answer
44 views

Securing fingerprint templates stored on web authentication server

I have a multi-factor web authentication server, that in addition to regular passwords uses fingerprints for user authentication. Can anyone think of a security flaw in the following scenario: I ...
0
votes
1answer
97 views

Bitdefender Antivirus SSL Cert substitution

I am using Bitdefender AV 2013 ed and I have noticed that when the Scan SSL is enabled in the configuration BD will use a local certificate, as mentioned here. This modifies the cert chain with BD as ...
0
votes
1answer
54 views

Will obtaining password hash compromise derived encryption key?

I've been looking at how PBKDF is used to generate encryption key for AES. One thing I couldn't get my head around is that how those OS keep the encryption key safe apart from using hardware modules. ...
0
votes
4answers
110 views

Using a Public-Key-Encryption browser side to avoid PCI compliance

We're developing a web application in which certain not logged users (clients) need to send their credit card details to other users (merchants) - which, we'll assume, are PCI compliant. We are ...
0
votes
1answer
54 views

Uniqueness of name in cryptography

If I publish my public key (I think I understand how this works, I'm still learning encryption) and I have a common name, could this leas to problems at all? OR does the email part guarantee that this ...
43
votes
1answer
3k views

How does a SIM card prevent cloning?

I have read a few articles about SIM cards, stating that the chip inside them uses some cryptographic magic to prevent people from cloning your number. This to me seems borderline impossible, given ...
2
votes
2answers
81 views

Related-password hash security

Say we are given a strong cryptographic hash function hash(), a strong completely random password of 15 characters pass15, two single-character salt values salta, saltb. We compute the hashes hasha, ...
0
votes
2answers
63 views

Is there something similar to pseudorandom generators but in the opposite direction?

Pseudorandom generators (PRG) are functions that takes a random small input (called the Seed) and maps it into much larger output . However, the mapping process must be unpredictable in order for the ...
0
votes
2answers
69 views

How to generate a superkey to decrypt strings

I'm working on an application where users have a key or password generated by me that is used to encrypt a string. Each user has their personal key, and no user should be able to decrypt another ...
1
vote
1answer
94 views

How easy is it to crack this encryption algorithm? [closed]

When I was about 13 or 14 years old, I was a little interested in cryptography (which is, after all, an interesting field). I learnt quite a lot since that time (it has been about 8 years since then), ...
0
votes
1answer
31 views

Can any ECC field element be safely serialized as “compressed” and then restored as uncompressed?

I have a library that stores all its ECC Field Elements in uncompressed form, in a bloated Base64 XML format, and storage has become a concern. (We want to support QR code as a form factor,etc) ...
2
votes
1answer
62 views

Would it be possible to add additional files to a password protected zip 2.0 file

So the scenario is this: I don't have the ability to determine/recover the master password for a production system that uses zip 2 archives. However, I need to be able to add new files to existing ...
2
votes
2answers
92 views

What problem does ECC seek to fix compared to RSA?

Elliptical Curve Cryptography (ECC) is one of the newest encryption schemes to challenge RSA cryptography. What problem does ECC seek to fix compared to RSA? Would you have any qualms with using ECC ...
0
votes
1answer
32 views

In TLS1.2 AES-GCM mode, what happened when input is not exactly the multiple of its block size?

I know that AES-GCM mode does not need padding, and its output are exactly the length of input data plus the tagging. But I am a little bit lost, as AES itself is block cipher, it could only operate ...
-2
votes
1answer
121 views

good books for learning network and web security? [closed]

I am reading "Hacking The Art of Exploitation" book . i have read till chapter 2 programming but most of it has gone above my head . I want to learn basically cryptography , network security and web ...
0
votes
2answers
96 views

Cryptography protocol suitable for two-way radio communications

Specifically talking about walkie talkie radio networks. Suppose there is a group of up to 16 persons, each equipped with such a unit. Typically, one person will be talking with one another ...
0
votes
0answers
31 views

Mobile App Processing Debit Card Transactions

I am creating a mobile app for iPhone and Android and the respective API that will be exposed to support the operations. This operations will require the customer to type the PIN to complete the ...
0
votes
2answers
85 views

What is the collision likelihood of MD5 when non-numeric values are removed?

Start with a unique identifier String macAddress = "CC:3A:61:24:D6:96"; Hash the identifier via MD5 implementation String hash = md5(macAddress); //bd37f780e10244cf28810b969559ad5b Remove all ...
0
votes
1answer
32 views

–°ompromised client.p12 file in OpenVPN

I'm not clearly understand technologies behind OpenVPN, so I have a question about OpenVPN security: What if I have client.p12 (PKCS#12) file and this file was leaked (with export password) to some ...
2
votes
1answer
85 views

Properties of AES Encryption

First of all, I apologize if these questions can be answered using a web search, but I'm sort of a crypto noob and don't know what to search for. Given N AES encrypted messages (where the message ...
1
vote
1answer
44 views

What is the relationship between Suite B and FIPS 140-2?

What is the relationship between the Suite B algorithms and FIPS 140-2 certification? Does OpenSSL meet both criteria? From what I've read, it seems that OpenSSL's crypto library implements many ...
1
vote
2answers
248 views

What's the point of the nonce in CTR mode?

Does having a nonce in CTR mode actually improve security (vs. just using 1, 2, 3, etc. - basically a constant nonce of 0)? As far as I can tell, the best-case scenario security-wise is that the ...
5
votes
3answers
111 views

AES256, repeated IVs and mostly-costant payload: how ok/bad is that?

I recently came across an application that more or less does this: starts from a (supposedly unknown to others) key generates a random IV encrypts some smallish (~ 160 bytes) payload with the key ...
3
votes
1answer
103 views

When to use HMAC alongside AES?

One of my clients wants to provide an URL to each of his customers to register in a system. This URL would contain a query string parameter with some data (e.g. code, email and name) from his clients ...
0
votes
0answers
62 views

How to secure my REST API once user authenticates with Google on mobile client?

In my application, I build REST APIs so that user can interact with my application server. Since I do not want to maintain User/Passwords, my iOS app authenticates client using Google. This all ...
0
votes
2answers
247 views

Reversible Hash Function?

Is there any reversible hash function? The hash function like SHA and MD5 are not reversible. I would like to know if there exist some reversible hash functions?
3
votes
1answer
52 views

What crypto prevents & detects “invisible” CAs? (e.g. in X509v4)

For this question, I'm calling an "invisible CA" one that Is signed by a root ca and exists as a 2nd or 3rd tier Is valid, not expired or revoked Has a different Public key than one that is ...
0
votes
1answer
70 views

Linux SSH and GPG

Can anyone please give me a quick crash course on SSH and GPG? SSH: What is the difference between public and private keys? Should I back up my ~/.ssh/ directory, what are the security implications ...
1
vote
0answers
24 views

How does OTR's authentication using “Question and answer” protect against MiTM?

I've read that the answer has something to do Socialist Millionaire, but I still don't understand how can the user be protected against malicious Man In The Middle, which would capture the question ...
0
votes
2answers
65 views

What are the alternatives to ECDSA for an authentication protocol?

In an authentication protocol, S has a public/private key pair known to C, and S and C have established a secure channel (for example, using DH or ECDH, or any other key exchange protocol). C wishes ...