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TLS and Ciphers Suites

The Concepts

TLS is initiated with a **handshake,** which after complete, the connection is considered secure for information exchange. Due to this TLS establishes a **stateful** connection.

The handshake utilizes both **asymmetric** and **symmetric** cryptography. The asymmetric keys are the public-private key-pair of the **X.509v3 certificate **which the server presents to the client.

By using this certificate, the client can **authenticate** the server. By verifying whether the certificate has been signed by a trusted **Certificate Authority (CA)**, the trust of the CA is extended to the server. If the client also has a certificate, the server may verify the identity of the client as well in a similar manner.

Cipher Suites

Cipher suites are made up of several components:

**Key Exchange Algorithm**: How the symmetric keys will be exchanged**Authentication Algorithm**: How the authentication of the server and optionally the client will be performed**Data Encryption Algorithm**: How the symmetric key will be used to encrypt the data**Message Authentication Algorithm**: How the connection will perform integrity checks

Key Exchange

Authentication

Data Encryption

Message Authentication

RSA

RSA

AES

MD5

DH

ECDSA

ChaCha20

SHA256

ECDH

PSK

DES

POLY1305

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// KeyExchange-Auth-Encrypton-MessageAuth

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ECDHE-ECDSA-AES128-GCM-SHA256

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ECDHE-RSA-AES128-GCM-SHA256

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ECDHE-ECDSA-AES256-GCM-SHA384

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ECDHE-RSA-AES256-GCM-SHA384

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ECDHE-ECDSA-CHACHA20-POLY1305

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ECDHE-RSA-CHACHA20-POLY1305

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DHE-RSA-AES128-GCM-SHA256

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DHE-RSA-AES256-GCM-SHA384

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**Symmetric Block Ciphers**: DES, AES**Symmetric Stream Ciphers**: ChaCha20, RC4**Asymmetric Ciphers**: RSA, DSA, DH, ECDH

AES encrypts blocks of 128-bits using a key of length 128, 192 or 256 bits while DES encrypts blocks of 64-bits. Stream ciphers on the other hand encrypt bit by bit.

Transport Layer Security (TLS) Parameters

FIPS 140-2 Compliant Randomness Tests

Randomness shouldn't be left to chance - HOWTO -LinuxCertified, Inc.

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$ cat /dev/urandom \ rngtest -c 100000

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rngtest 5

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Copyright (c) 2004 by Henrique de Moraes Holschuh

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This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

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rngtest: starting FIPS tests...

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rngtest: bits received from input: 2000000032

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rngtest: FIPS 140-2 successes: 99927

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rngtest: FIPS 140-2 failures: 73

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rngtest: FIPS 140-2(2001-10-10) Monobit: 13

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rngtest: FIPS 140-2(2001-10-10) Poker: 9

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rngtest: FIPS 140-2(2001-10-10) Runs: 26

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rngtest: FIPS 140-2(2001-10-10) Long run: 25

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rngtest: FIPS 140-2(2001-10-10) Continuous run: 0

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rngtest: input channel speed: (min=5.989; avg=707.717; max=19073.486)Mibits/s

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rngtest: FIPS tests speed: (min=18.393; avg=180.330; max=200.774)Mibits/s

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rngtest: Program run time: 13286865 microseconds

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https://www.researchgate.net/publication/340726126_On_the_unbearable_lightness_of_FIPS_140-2_randomness_tests

www.researchgate.net

"Concretely, this work illustrates the inability of the FIPS 140 family of tests to detect bias in three obviously flawed PRNGs." -On the unbearable lightness of FIPS 140-2 randomness tests,DOI:10.1109/TIFS.2020.2988505

Block Cipher: Mode of Operation

"A mode of operation describes how to repeatedly apply a cipher's single-block operation to securely transform amounts of data larger than a block" -WIkipedia"Block cipher modes of operation have been developed to eliminate the chance of encrypting identical blocks of text the same way" -WolfSSL

Mode of operations are general

Confidentiality-only modes

Examples of modes:

- ECB
- CBC
- CFB
- OFB
- CTR

AE and AEAD modes

In contrast to confidentiality-only modes, **Authenticated Encryption (AE) **schemes ensure both confidentiality and data authenticity.

By utilizing AE, the algorithm can recognize improperly-constructed ciphertexts and refuse to decrypt them. This prevents an attacker from requesting the decryption of any ciphertext unless it was generated using the encryption algorithm with knowledge of the plaintext and the key.

Examples of modes:

- GCM - widely used in TLS.
- CCM

- "
*Reusing an IV with the same key in CTR, GCM or OFB mode results in XORing the same keystream with two or more plaintexts, a clear misuse of a stream, with a catastrophic loss of security.*"

Last modified 3mo ago