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Questions tagged [tls]

SSL (Secure Sockets Layer) and its successor TLS (Transport Layer Security) are protocols which provide communication security (privacy and integrity) for a bidirectional data channel.

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Is there a standard for OpenSSL-interoperable AES encryption?

Many AES-encrypted things (files, strings, database entries, etc.) start with "Salted__" ("U2FsdGVkX1" in base64). I hear it's ...
David Cary's user avatar
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11 votes
1 answer
3k views

Why Static RSA and Diffie-Hellman cipher suites have been removed in TLS 1.3?

Why Static RSA and Diffie-Hellman cipher suites have been removed in TLS 1.3? How keys can be exchanged then? https://datatracker.ietf.org/doc/html/draft-ietf-tls-tls13-28
Nathan Aw's user avatar
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6 votes
2 answers
4k views

GMAC vs HMAC in message forgery and bandwidth

Saarinen in his work GCM, GHASH and Weak Keys says that: The GHASH algorithm belongs to a widely studied class of Wegman-Carter polynomial universal hashes. The security bounds known (this and ...
kelalaka's user avatar
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52 votes
7 answers
33k views

Google is using RC4, but isn't RC4 considered unsafe?

Why is Google using RC4 for their HTTPS/SSL? $ openssl s_client -connect www.google.com:443 | grep "Cipher is" New, TLSv1/SSLv3, Cipher is RC4-SHA Isn't RC4 ...
Jonas Lejon's user avatar
9 votes
1 answer
3k views

The 9 lives of Bleichenbacher's CAT, it puts another scratch again

Bleichenbacher demonstrated a padding oracle attack against RSA implementations that follow the PKCS #1 v1.5. Through the years, there are various mitigation techniques developed as OAEP and limiting ...
kelalaka's user avatar
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24 votes
3 answers
39k views

How can Cipher Block Chaining (CBC) in SSL be attacked?

I am trying to understand how CBC-mode in SSL/TLS can be attacked. I have been looking around online but all examples and explanations are very hard to understand and follow. Can you give a simple ...
antonpug's user avatar
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23 votes
2 answers
20k views

What is the purpose of four different secrets shared by client and server in SSL/TLS?

I was looking through the working of SSL V3, and found that a connection state is defined by a set of things, including client write mac secret, server write mac secret, server write key, client ...
user5507's user avatar
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15 votes
2 answers
2k views

Does a trace of SSL packets provide a proof of data authenticity?

I'm wondering if it would make sense to record a whole HTTPS session, publish its encryption keys and present it to third parties as a proof that this particular data was sent by a given server ...
d33tah's user avatar
  • 363
8 votes
1 answer
941 views

Cipher suites: same name, different IDs, why?

Sorry if I missed with a community to ask. Recently I stumbled on a fact that the same cipher suite can be designated by two different IDs, and this is not a typo nor single occasion. For instance: ...
Yury Schkatula's user avatar
39 votes
3 answers
11k views

Why was AES CBC removed in TLS 1.3?

I don't quite understand why AES CBC was removed in TLS1.3. From what I know CBC is the most secure Mode of operation for the AES block cipher (if you can say it like that). It only needs a TRND IV ...
Richard R. Matthews's user avatar
7 votes
4 answers
3k views

Is encrypted e-mail sent over TLS 1.3 a form of "forward secrecy" (similar to something like Signal)?

One common complaint about GPG-encrypted e-mail is that it doesn't provide forward secrecy; however with opportunistic TLS becoming increasingly common in both IMAP and SMTP, it's not unreasonable to ...
philomathic_life's user avatar
87 votes
5 answers
280k views

How secure is AES-256?

The cipher AES-256 is used among other places in SSL/TLS across the Internet. It's considered among the top ciphers. In theory it's not crackable since the combinations of keys are massive. Although ...
Gustav's user avatar
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45 votes
3 answers
39k views

Is Triple DES still considered safe to use?

What it says on the tin. Is it still used in things like TLS?
Melab's user avatar
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12 votes
5 answers
17k views

Why do we need asymmetric algorithms for key exchange?

In SSL protocols, both symmetric and asymmetric algorithms are used. Why is it so? The symmetric algorithms are more secure and easier to implement. Why are asymmetric algorithms usually preferred in ...
user5507's user avatar
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9 votes
1 answer
7k views

Why does AES-GCM need a hash/MAC in TLS?

"TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256" is just one example for a cipher suite, as far as I'm concerned it means this: It uses the TLS protocol, exchanges keys with Elliptic Curve Diffie Hellman ...
hl3mukkel's user avatar
  • 499
4 votes
1 answer
258 views

Are HTTPS web sessions non-repudiable?

(This is probably a basic question, and may be a duplicate; if so, just let me know.) Suppose there are two clients A and B, ...
DumpsterDoofus's user avatar
44 votes
5 answers
167k views

What is the SSL private key file format?

I was researching about how to encrypt with RSA. I understood everything but not the format of the private keys. In the phpseclib (RSA in PHP), you can import your private key (private.key format) ...
tor's user avatar
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9 votes
1 answer
6k views

SHA1 no longer considered secure for SSL Certificates -- what about Cipher Suites?

Many browsers and Internet companies have recently claimed that SSL Certificates with a signature algorithm of SHA1 will imminently no longer be considered secure. Most notably, Google and Google ...
Eddie's user avatar
  • 983
148 votes
1 answer
239k views

What are the differences between .pem, .csr, .key, .crt and other such file extensions?

I'm new to SSL / TLS, and I want to work with the OpenSSL toolkit. What do .pem and .csr stand for? I do know that ...
Richard R. Matthews's user avatar
23 votes
2 answers
29k views

Why is TLS susceptible to protocol downgrade attacks?

A recent blog post from Ivan Ristić (expert extraordinaire on all things SSL) says: all major browsers are susceptible to protocol downgrade attacks; an active MITM can simulate failure conditions ...
D.W.'s user avatar
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14 votes
2 answers
17k views

What's the GCM-SHA 256 of a TLS protocol?

If we read the Google line information about how the cypher the https communication, it reads: TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 I understand it's using ...
MyUserIsThis's user avatar
5 votes
2 answers
3k views

Why does TLS do Authenticate-then-Encrypt instead of Encrypt-then-Authenticate?

Encrypt-then-Authenticate (EtA) seems to generally be considered the better option, compared to Authenticate-then-Encrypt (AtE) (see this Crypto.SE question, for example). The people writing the RFC ...
malexmave's user avatar
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4 votes
2 answers
3k views

Which block cipher mode of operation does TLS 1.3 use?

Which block cipher mode of operation does TLS 1.3 use? I assume it is a block cipher mode that provides authentication (like GCM).
Abra Cadabra's user avatar
4 votes
1 answer
2k views

Static Diffie-Hellman in TLS

Static Diffie-Hellman (cipher suites with DH in their name but neither DHE or DH_anon - ...
blabla_trace's user avatar
63 votes
5 answers
101k views

What's the appeal of using ChaCha20 instead of AES?

I read about ChaCha20 being used in TLS by Google, SSH, and towards standardization in general. What's the appeal of using something other than AES, what with AES receiving dedicated CPU instructions ...
JDługosz's user avatar
  • 733
28 votes
3 answers
39k views

How can I use SSL/TLS with Perfect Forward Secrecy?

I'm new to the field of cryptography, but I want to make the web a better web by setting up the sites that I host with Perfect Forward Secrecy. I have a list of questions regarding the setup of ...
Clay Freeman's user avatar
21 votes
2 answers
22k views

What is the advantage of AEAD ciphers?

What is the advantage of AEAD ciphers? Why is the TLS working group pushing for them? I thought modern cipher suites require SHA256 for authentication. What advantage is there to including Poly1305? ...
user3201068's user avatar
20 votes
2 answers
9k views

Why do new versions of TLS use an explicit IV for CBC suites?

SSL 3.0 and TLS 1.0 used an insecure scheme to generate implicit IVs when encrypting records in CBC mode: they used the last part of the previous record, a value that can be predicted by the attacker. ...
CodesInChaos's user avatar
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19 votes
1 answer
5k views

Will IBM's Condor quantum processor run Shor's Algorithm to crack a 256-bit Elliptic Curve key?

Yesterday IBM announced that they have a 433 bit quantum computer, called Osprey. There is nothing in the press releases I can find that says whether it can or cannot run Shor's Algorithm. They also ...
Simon G.'s user avatar
  • 343
14 votes
2 answers
12k views

What's the difference between rsa_pss_pss_* and rsa_pss_rsae_* schemes?

I'm trying to understand the difference between rsa_pss_pss_ and rsa_pss_rsae_. The picture shows the extension of TLS1.3's ...
Nail Jay's user avatar
  • 317
10 votes
3 answers
9k views

What is different below two Ciphersuites?

I have two questions; I need an explanation for the differences of below two cipher suites. How do they work with SSL/TLS protocol? (my main concern first one doesn't have '...
uma's user avatar
  • 231
9 votes
1 answer
13k views

What is the purpose of pre master secret in SSL/TLS?

I studied about SSL/TLS and learned that client and server must share keys below. common key for encryption common key for generating message authentication code Then, in SSL/TLS, a client doesn't ...
moriteru's user avatar
7 votes
1 answer
892 views

Does TLS use RC4-drop[n]?

According to many sources, the first few (n) bytes of the RC4 keystream are strongly biased, and therefore should be discarded before using the keystream to encrypt anything; this precaution is ...
lxgr's user avatar
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7 votes
4 answers
4k views

The difference between MACs vs. HMACs vs. PRFs

I have some confusion regarding the difference between MACs and HMACs and PRFs and when to use which term. If the function is computed using a hash and secret key like the following, is this a HMAC ...
user6875880's user avatar
6 votes
1 answer
1k views

Why is TLS SRP verifier based on user name?

I don't understand why TLS SRP (or SRP in general) includes the user name in verifier calculation, given that user name is basically public. From spec RFC 5054 $x$, which is then used to calculate ...
nefarel's user avatar
  • 183
5 votes
2 answers
9k views

What does the TLS 1.2 client finished message contain?

I am implementing TLS 1.2 and I'm stuck on the client finished message. My question is: what is the size and structure of a clients finished message in TLS 1.2 when using the ...
Ahsan's user avatar
  • 59
5 votes
3 answers
1k views

Does the XML Encryption flaw affect SSL/TLS?

A "practical attack against XML's cipher block chaining (CBC) mode" has been demonstrated: XML Encryption Flaw Leaves Web Services Vulnerable. Does this weakness of CBC-mode which is used here also ...
zimdanen's user avatar
  • 153
4 votes
2 answers
8k views

Why is a Diffie-Hellman key exchange required when RSA is already being used for key exchange in TLS?

Specifically with TLS, What is RSA used for during key exchange? What is Diffie-Hellman used for? Since RSA already provides authenticity and confidentiality, why is Diffie-Hellman used during the ...
wispi's user avatar
  • 203
4 votes
1 answer
4k views

Clarification needed in TLS 1.2 key derivation process

Reference to TLS 1.2 standard documentation section 6.3 regarding the key generation here: To generate the key material, compute ...
user6875880's user avatar
3 votes
1 answer
652 views

How does padding oracle attack work with bytes larger than possible length?

I am trying to understand how the POODLE attack would actually be implemented. In the original security advisory from Möller, Duong and Kotowicz [POODLE 14] the following example is presented: Assume ...
rtur's user avatar
  • 33
3 votes
1 answer
570 views

Can I reduce the MAC size in TLS?

The MAC size is reduced to 80 bits in truncated_hmac extension , which says "forging of MAC values cannot be done off-line: in TLS, a single failed MAC guess will cause the immediate termination ...
wub's user avatar
  • 223
3 votes
1 answer
2k views

On what basis is padding chosen in OpenSSL?

I am using CAPI Engine in OpenSSL and I did some test. When I use TLS 1.0 or 1.1, during handshake and RSA signing, PKCS padding is chosen. When I use TLS 1.2, RSA signing uses PSS padding. What ...
archangel's user avatar
2 votes
1 answer
471 views

What hash is concatenating with the data to be signed in TLS 1.3 CertificateVerify message?

According to specification, to create data that will be signed with server private key for CertificateVerify message, we need to concatenate 64 space characters, the string "TLS 1.3, server ...
Iceman's user avatar
  • 137
2 votes
1 answer
786 views

Is AES-256 over AES-128 weakening the original encryption?

When transfering data using TLS the browser and server agree the cipher suite to be used - so for example this could be chosen as AES-128 and is (probably) outside of my control. If I separately ...
Bob's user avatar
  • 21
2 votes
0 answers
85 views

Is my way safe to remove SSL CA Cert by DHT and PoW NodeID for a decentralized system?

To implement a decentralized system, I wrote a TLS like P2P net stack. The main idea is removing CA Cert from the whole system by using a DHT for Naming and Key Exchange. I am not a crypto expert, so ...
auxten's user avatar
  • 121
1 vote
1 answer
430 views

Verify authenticity of TLS/HTTPS communication

I have a question regarding https/tls. Lets say a client requests a website from a server via https. The client stores the entire traffic and his secrets to disk. Can i afterwards verify the ...
user avatar
0 votes
0 answers
222 views

TLS 1.2 finished message stucture [duplicate]

I am implementing TLS 1.2 and using ECDHE_RSA_AES_128_GCM_SHA256 cipher suit. According to RFC 5246 finished messages have {verify_data[verify_data_length]} and verify_data = PRF(master_secret, ...
Ahsan Younis's user avatar
49 votes
2 answers
80k views

Differences between the terms "pre-master secret", "master secret", "private key", and "shared secret"?

Both crypto.SE and security.SE have excellent Q&As about how TLS generates session keys (I have linked some at the bottom). In reading these threads I'm having troubles with terminology since the ...
Mike Ounsworth's user avatar
27 votes
2 answers
2k views

Why did TLS 1.3 prohibit PGP authentication?

There is a specification, in Informational(!) RFC 6091, for using PGP keys in TLS authentication, although I don’t think it has ever been implemented outside of GnuTLS (it’s certainly not in OpenSSL). ...
Alex Shpilkin's user avatar
18 votes
1 answer
5k views

Why does TLS 1.3 support two CCM variants?

One of the important improvements introduced in TLS 1.3 is the pruning of the many previously available cipher suites to only five secure options (for symmetric ciphers), that are each supposed to ...
AardvarkSoup's user avatar