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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49
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7answers
31k 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 ...
5
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2answers
1k 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 ...
21
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3answers
33k 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 ...
8
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1answer
1k 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 ...
13
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4answers
8k views

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 ...
18
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2answers
16k 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 ...
7
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4answers
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 ...
10
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1answer
1k 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://tools.ietf.org/html/draft-ietf-tls-tls13-28
79
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5answers
266k 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 ...
9
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1answer
5k 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 ...
8
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1answer
439 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: ...
37
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3answers
7k 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 ...
13
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2answers
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 ...
8
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1answer
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 ...
41
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5answers
128k 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) ...
39
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2answers
28k views

Is Triple DES still considered safe to use?

What it says on the tin. Is it still used in things like TLS?
23
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2answers
26k 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 ...
9
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5answers
15k 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 ...
9
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2answers
9k 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 ...
5
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2answers
2k 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 ...
4
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1answer
158 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, ...
4
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1answer
597 views

Static Diffie-Hellman in TLS

Static Diffie-Hellman (cipher suites with DH in their name but neither DHE or DH_anon - ...
76
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1answer
116k views

What is the difference between .pem, .csr, .key and .crt and other such file extensions?

I'm new to SSL / TLS and I want to work with the OpenSSL toolkit. I don't know what .pem and .csr stands for? I do know that <...
43
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2answers
48k 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 ...
27
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3answers
38k 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 ...
18
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2answers
16k 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? ...
11
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2answers
4k 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 ...
20
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2answers
7k 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. ...
5
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4answers
2k 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 ...
9
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1answer
9k 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 ...
7
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1answer
727 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 ...
5
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3answers
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 ...
4
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1answer
2k 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 ...
4
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2answers
5k 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 ...
2
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1answer
699 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 ...
3
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1answer
460 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 ...
3
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1answer
387 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 of ...
2
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0answers
52 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 ...
0
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0answers
208 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, ...
11
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2answers
17k views

At what stage is DHE and RSA used during the SSL/TLS handshake?

At what stage of the SSL/TLS handshake is the DHE and RSA used and what is the purpose of using a pre-master secret when you could just use RSA to exchange the symmetric key (i.e. AES) for further ...
43
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5answers
57k 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 ...
14
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1answer
6k views

Why is CAMELLIA suddenly so widely used?

When nowadays I point my browser to https sites, the cipher that is on most occasions used is Camellia. My browsers (Chrome and Firefox) seem to prefer it, even when AES is available. Is that not ...
7
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2answers
16k views

With OpenSSL and ECDHE, how to show the actual curve being used?

Using openssl s_client -host myserver.net -port 443 I can see the cipher negotiated is indeed using ECDHE for session key ...
27
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2answers
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). ...
3
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1answer
2k views

How do TLS 1.1 and 1.2 generate IVs (initialization vectors) for each record?

According to RFC 4346 Explicit IVs [CBCATT] describes a chosen plaintext attack on TLS that depends on knowing the IV for a record. Previous versions of TLS [TLS1.0] used the CBC ...
7
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2answers
4k views

How key materials are generated in SSL V3 from master secret

The generation of key materials is given by ...
3
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3answers
8k views

How is session key generated for TLS?

I would like to understand better what happens during establishment of SSL/TLS secure connection. The Client wants to establish a connection - ClientHello The server answers with a ServerHello. This ...
2
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1answer
1k views

SSL-like protocol with public-key hard-coded in the client

Imagine a SSL-like protocol that instead of using certificates signed by a trusted CA, has the server's public key hard-coded in the client. My question is: what happens if the server's private key is ...
14
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1answer
3k views

What is wrong with AES-CTR-HMAC-SHA256 - or why is it not in TLS?

It seems the only specified CTR mode ciphers in TLS are all GCM based. GCM ciphers run AES-CTR and do authenticated encryption with a MAC based on Galois-field ...
5
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0answers
1k views

How does TLS differ from SSH from a strictly cryptographic perspective?

How does TLS differ from SSH from a strictly cryptographic perspective? I know that there are many non-cryptographic differences between them, but I would like to know the cryptographic ones.