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Results tagged with hmac
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user 655
a method for constructing a message authentication code based on a cryptographic hash function.
2
votes
Does the HMAC of symmetric key revealed weakens the encryption?
In practice, though, HMAC is safe for that. …
- 329k
1
vote
Why can't a cryptographic hash inside a cryptogram serve as a MAC?
Appending the hash then encrypting the whole lot is not necessarily secure. Actually, depending on the encryption system, it may be awfully weak. For instance, suppose that encryption is done with a s …
- 329k
2
votes
Proper hash_hmac key creation
HMAC uses as key a sequence of arbitrary bytes and of arbitrary length. Some implementations of HMAC/SHA-256 may (unduly) reject keys longer than 32 bytes. …
- 329k
4
votes
Accepted
Reusing HMAC state for multiple messages
Other constructions are possible, such as using the previous HMAC value (you send "m,HMAC(k, z || m)" where z is the HMAC output sent with the previous message). … (The ability of HMAC to operate in an IV-less fashion is the feature which makes it the best generic MAC algorithm. …
- 329k
3
votes
Accepted
How do I build a secure signing mechanism on top of HMAC
Technically, HMAC is a MAC, not a signature. … In particular, the attacker cannot guess the HMAC key, because obtaining the HMAC key would allow him to create a lot of forgeries. …
- 329k
4
votes
Accepted
Determining strength of truncated HMAC
known value+HMAC pairs). … bogus HMAC value (as you do). …
- 329k
3
votes
Accepted
does validating MAC of individual packets validates the integrity of whole file?
The MAC in SSL/TLS is computed over the combination of the record payload and a sequence number, thus ensuring that records are all received, with no missing, out-of-order or duplicated record. The co …
- 329k
4
votes
Accepted
How to guarantee counter synchronisation between client and server for counter in hmac-based...
See HOTP, section E.4. This is reasonably well explained. The gist of the solution: when the counter on the server contains n, the server actually accepts as valid the one-time passwords corresponding …
- 329k
16
votes
Accepted
HOTP with as HMAC hashing algoritme a hash from the SHA-2 family
HMAC/SHA-1 is not broken. … But HMAC resistance does not rely on resistance to collisions. …
- 329k
7
votes
Accepted
Should password hashes be encrypted or HMACed?
Encryption, or a deterministic MAC, may offer you an extra gain of security on the off-chance that the attacker could grab the database of hashed-and-encrypted passwords but not the encryption/MAC key …
- 329k
8
votes
Accepted
Can a salted hash be an effective MAC?
Which is precisely why HMAC was invented: with its double-nested hash invocation, it copes with the non-random-oracleness of MD hash functions. … If you need Performance with a big 'P', the kind which would not be fulfilled by HMAC, then:
You have very fast networks, or very slow CPU. …
- 329k
5
votes
Accepted
How do I transfer the HMAC?
Combining MAC and encryption is hard. Depending on how you do it, the result will be secure, or not, or only "mostly secure" modulo a zillion of implementation details. GCM is an Authenticated Encrypt …
- 329k
1
vote
Detect message tampering without shared key and without certificate authority
To detect tampering, you first have to define tampering. You are receiving a message; what would make it a "tampered" message and not the "genuine" message ?
The usual definition of tampered/genuine …
- 329k
35
votes
Accepted
Why a symmetric key for HMAC?
When a HMAC value is successfully verified, the Amazon server is convinced that someone knowing the HMAC key was involved; since that key is known only to the client and the server itself, and the server … More complexity: mathematics and code involved in digital signatures are more complex than HMAC (HMAC is just a pair of hash function invocations; digital signatures begin with a hash function invocation …
- 329k
12
votes
Accepted
NIST test vectors for HMAC-SHA-256
Including for HMAC (near the end of that page). In the file contained in the Zip archive, the vectors for HMAC/SHA-256 ought to be the ones with the parameter "L=32". …
- 329k