Questions tagged [ephemeral]

Ephemeral defines things that are short-lived, like (for example) an ephemeral key, which is a key that only exists within the lifetime of a communication session.

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Signal Protocol - Better way to generate one time pre keys (OTPK)

The following explains a different way (then one time pre keys) for Bob to securely generate ephemeral keys asynchronously without a limit while still being able to delete the private key immediately ...
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2answers
293 views

Are ephemeral keys symmetric or asymmetric? [closed]

My question is: Are ephemeral keys symmetric or asymmetric? If symmetric, can ephemeral keys be created based on a (UserID || nonce)?
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Zero Knowledge Proof of Association

Assuming there are a group of individuals with static ecdsa keypairs, of which the public keys are in a shared database that all of them have access to, how can each participant publish an ephemeral ...
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1answer
59 views

Emphemeral key creation from a long term shared secret (without DH)

Assuming I cannot use DH scheme, and the long term key is known to both sides, is there a known algorithm / standard that defines how to derive a short term key from a long term key?
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54 views

Verion of crypto_box() which doesn't allow the sender to decrypt previously sent messages

Libsodium's crypto_box() family of functions allow the sender to send messages using its public/private keypair knowing the receiver's public key, and allow the ...
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2answers
587 views

What is the difference between a sealed box and a normal box in libsodium?

I'm trying to learn libsodium to better my crypto knowledge. One nagging question I have is what is the difference between libsodium's sealed box and their normal box? Not in terms of technicalities ...
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Misuse-resistant ephemeral key exchange?

This recent question had me the idea to ask: is there a "misuse-resistant ephemeral key exchange"? At first sight, this seemed self-contradictary - ephemeral implies there's a random part, while ...
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Purpose of signed prekey in X3DH? [duplicate]

In the X3DH protocol a signed prekey ($SPK_B$) is used as part of the handshake. What is the purpose of this key? There seem to be no obvious cryptographic drawbacks by omitting this key. One ...
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1answer
410 views

How to correctly evaluate the security of DH in TLS

I'm trying to understand and evaluate the security impact of DH in TLS. As far as I can tell, there are four major different implementations of DH in TLS. DH DHE ECDH ECDHE With the ephemeral DH's, ...
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1answer
195 views

What are the consequences (and potential mitigation) to poor entropy/RNG on server-side during ephemermal key generation and DH exchange

I am using a hardware TRNG feeding the entropy pool on the client side. But, in a world of virtualized, headless server hosts, what are the cryptographic/security consequences for random numbers (or a ...
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1answer
1k views

Does perfect forward secrecy (using DH or ECDH) imply quantum resistance?

Does perfect forwarding secrecy, as used for e.g. the DHE_ and ECDHE_ TLS ciphersuites make it impossible for quantum analysis ...
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1answer
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What's the difference between DH and DHE?

The DH equation is: $$ K = g^{xy} \bmod p$$ Does using DHE mean even the $g$ and $p$ parameters are randomly generated (instead of being fixed)? Is this the difference?
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406 views

Ephemeral Encryption Keys

My understanding is, ignoring implementation details, iOS disk encryption works like this: On boot (and/or every time you unlock your phone) an ephemeral session key is created that can decrypt ...
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1answer
430 views

Forward Secrecy when using non-ephemeral DH

In context SSL/TLS, reading up on various sites, I find forward secrecy in DH key exchange being linked to its ephemeral use i.e. DHE. I don't fully understand this link, where does following ...
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3answers
710 views

Authenticate ephemeral key exchange

At the moment I'm designing a crytosystem for a VPN server. One of the requirements is Perfect Forward Secrecy, but I'n not sure how to implement authentication on the ephemeral key exchange. If both ...
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1answer
134 views

Ephemeral Diffie-Hellman in a symmetric crypto context

I'd like forward secrecy in a case where the two sides have a shared long-term symmetric key. I intend to use AES in GCM. It looks like ephemeral Diffie-Hellman is the best way to generate the session ...
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Diffie–Hellman Ephemerality Nomenclature

Below is a short excerpt of available DH cipher suites available on a machine. I understand EDH is ephemeral DH, and that ECDH is for Elliptic-Curve DH which is computationally faster. ECDHE is both ...
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1answer
337 views

Ephemeral Diffie-Hellman generator selection

I need to generate a EDH group on the fly in one has not been specified in a config file. Diffie-Hellman is kind of expensive in terms of computation, so I'd like to reduce the cost if possible. Is ...