HMAC is a method for constructing a message authentication code based on a cryptographic hash function.

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What is a simple information authentication protocol for constrained devices?

Background: I have an application where devices will poll information from some source on the network. These devices are very basic and have modest processing and memory capabilities. Hashing (and ...
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How to make a “zero knowledge” cache/key-value store

I'd like to use a possibly insecure cache for storing expensive-to-calculate sensitive information. My requirements are: If the cache ever gets compromised it should reveal nothing about its ids or ...
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Why does HMAC use two different keys?

Suppose $H$ is a hash function; why is $H(k||H(k||m))$ not secure? See this HMAC definition. In there, indeed two keys are used and the mac algorithm is $H(k_1 ||H(k_2 ||m))$ . Why don't we use $H(k||...
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When do I need to renew keys for Salsa20 or HMAC?

I currently have a system which uses two keys sourced from a single key subjected to HKDF. One key is used in the Salsa20 stream ...
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If a PRG is constructed by iterating a PRF, is it backtracking-resistant?

Say we construct a pseudo-random number generator from a pseudo-random function $f$ (using some constant key $k$ and some initial value $v_0$). We do this by feeding the output block of the PRF back ...
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DPA Attack on HMAC SHA-256

I have read the paper Differential Power Analysis of HMAC SHA-2 in the Hamming Weight Model and I want to understand the DPA Attack. In section 3.2.1 Path 1 (page 4) there is written: The last ...
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How does use of HMAC affect hash function combiners?

In the comments of this question, Ricky Demer proposes a function $HMAX$ to combine two $HMAC$s based on different hash functions: $HMAX_{H0,H1}(⟨k_0,k_1⟩,m) = HMAC_{H0}(k_0,m) \oplus HMAC_{H1}(k_1,m)...
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Is it safe to use a key as message in keyed hashing (HMAC)?

Scenario: User gives password. A "password key" is derived from the password (e.g. by PBKDF2). A random salt is applied. The password key is hashed with a HMAC algorithm (e.g. HMAC-SHA256), with ...
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Keys and key-stretching when authenticating requests?

I'm making a REST application and still a bit confused about this issue. basically, to authenticate incoming requests, I give out userId, issued timestamp, expiry timestamp (normally 3 months after ...
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Is there any analysis of freebsd's “geli” encrypted geometry provider?

I've done a few obvious searches on google and google scholar and not turned up any security analysis of FreeBSD's geli. Is there some out there, or has it gone unanalyzed since its introduction ...
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PHP Apple News HASH HHMAC

I am having a problem generating the signature key in PHP as describred in the Apple nes API documentation found here: https://developer.apple.com/library/ios/documentation/General/Conceptual/...
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Length extension attacks or prefix attacks on HMAC

Why HMACs are not vulnerable to length extension attacks or prefix attacks? (As commented by @codesinchaos, That's a different construction. So it's related, but no duplicate of Why is H(message||...
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Implementing hmac+bcrypt in bash script

I was recently reading Mozilla's Secure Coding guidelines and found their password storage method interesting. They combine an hmac hash of the password with bcrypt which allows for added security ...
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What are the consequences of not checking the server mac in a TLS connection?

The context for this question (it's quite involved) can be found in this document: https://docs.google.com/file/d/0B15itpMWb2ztWTJrYTgzX204OVU However, I want to make it clear that you don't have to ...