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Common Cryptographic Flaw

Are initialization vectors ignored, reused, or not generated sufficiently secure for the cryptographic mode of operation? Is an insecure mode of operation such as ECB in use? Is encryption used when authenticated encryption is more appropriate?

Common Cryptographic Flaw

Is randomness used for cryptographic purposes that was not designed to meet cryptographic requirements? Even if the correct function is chosen, does it need to be seeded by the developer, and if not, has the developer over-written the strong seeding functionality built into it with a seed that lacks sufficient entropy/unpredictability?

Initialization vectors must be chosen appropriate for the mode of operation. For many modes, this means using a CSPRNG (cryptographically secure pseudo random number generator). For modes that require a nonce, then the initialization vector (IV) does not need a CSPRNG. In all cases, the IV should never be used twice for a fixed key.

Keys should be generated cryptographically randomly and stored in memory as byte arrays. If a password is used, then it must be converted to a key via an appropriate password base key derivation function.

Ensure that cryptographic randomness is used where appropriate, and that it has not been seeded in a predictable way or with low entropy. Most modern APIs do not require the developer to seed the CSPRNG to get security.

Scenario #1: An application encrypts credit card numbers in adatabase using automatic database encryption. However, this data isautomatically decrypted when retrieved, allowing a SQL injection flaw toretrieve credit card numbers in clear text.

Scenario #3: The password database uses unsalted or simple hashes tostore everyone's passwords. A file upload flaw allows an attacker toretrieve the password database. All the unsalted hashes can be exposedwith a rainbow table of pre-calculated hashes. Hashes generated bysimple or fast hash functions may be cracked by GPUs, even if they weresalted.

If n is 300 bits or shorter, it can be factored in a few hours in a personal computer, using software already freely available. Keys of 512 bits have been shown to be practically breakable in 1999, when RSA-155 was factored by using several hundred computers, and these are now factored in a few weeks using common hardware. Exploits using 512-bit code-signing certificates that may have been factored were reported in 2011.[35] A theoretical hardware device named TWIRL, described by Shamir and Tromer in 2003, called into question the security of 1024-bit keys.[33]

There is no known attack against small public exponents such as e = 3, provided that the proper padding is used. Coppersmith's attack has many applications in attacking RSA specifically if the public exponent e is small and if the encrypted message is short and not padded. 65537 is a commonly used value for e; this value can be regarded as a compromise between avoiding potential small-exponent attacks and still allowing efficient encryptions (or signature verification). The NIST Special Publication on Computer Security (SP 800-78 Rev. 1 of August 2007) does not allow public exponents e smaller than 65537, but does not state a reason for this restriction.

A cryptographically strong random number generator, which has been properly seeded with adequate entropy, must be used to generate the primes p and q. An analysis comparing millions of public keys gathered from the Internet was carried out in early 2012 by Arjen K. Lenstra, James P. Hughes, Maxime Augier, Joppe W. Bos, Thorsten Kleinjung and Christophe Wachter. They were able to factor 0.2% of the keys using only Euclid's algorithm.[38][39]

One way to thwart these attacks is to ensure that the decryption operation takes a constant amount of time for every ciphertext. However, this approach can significantly reduce performance. Instead, most RSA implementations use an alternate technique known as cryptographic blinding. RSA blinding makes use of the multiplicative property of RSA. Instead of computing cd (mod n), Alice first chooses a secret random value r and computes (rec)d (mod n). The result of this computation, after applying Euler's theorem, is rcd (mod n), and so the effect of r can be removed by multiplying by its inverse. A new value of r is chosen for each ciphertext. With blinding applied, the decryption time is no longer correlated to the value of the input ciphertext, and so the timing attack fails.

In 1998, Daniel Bleichenbacher described the first practical adaptive chosen-ciphertext attack against RSA-encrypted messages using the PKCS #1 v1 padding scheme (a padding scheme randomizes and adds structure to an RSA-encrypted message, so it is possible to determine whether a decrypted message is valid). Due to flaws with the PKCS #1 scheme, Bleichenbacher was able to mount a practical attack against RSA implementations of the Secure Sockets Layer protocol and to recover session keys. As a result of this work, cryptographers now recommend the use of provably secure padding schemes such as Optimal Asymmetric Encryption Padding, and RSA Laboratories has released new versions of PKCS #1 that are not vulnerable to these attacks.

My clients are reporting this error. I cannot reproduce it. What's more, I cannot detect any flaws: all report to have a valid cert. I've Google(ed) for ssl_error_no_cypher_overlap, but none of the threads provided any useful guidance.

Diffie-Hellman key exchange is a popular cryptographic algorithm that allows Internet protocols to agree on a shared key and negotiate a secure connection. It is fundamental to many protocols including HTTPS, SSH, IPsec, SMTPS, and protocols that rely on TLS.

Logjam attack against the TLS protocol. The Logjam attack allows a man-in-the-middle attacker to downgrade vulnerable TLS connections to 512-bit export-grade cryptography. This allows the attacker to read and modify any data passed over the connection. The attack is reminiscent of the FREAK attack, but is due to a flaw in the TLS protocol rather than an implementation vulnerability, and attacks a Diffie-Hellman key exchange rather than an RSA key exchange. The attack affects any server that supports DHE_EXPORT ciphers, and affects all modern web browsers. 8.4% of the Top 1 Million domains were initially vulnerable.

We carried out this computation against the most common 512-bit prime used for TLS and demonstrate that the Logjam attack can be used to downgrade connections to 80% of TLS servers supporting DHE_EXPORT. We further estimate that an academic team can break a 768-bit prime and that a nation-state can break a 1024-bit prime. Breaking the single, most common 1024-bit prime used by web servers would allow passive eavesdropping on connections to 18% of the Top 1 Million HTTPS domains. A second prime would allow passive decryption of connections to 66% of VPN servers and 26% of SSH servers. A close reading of published NSA leaks shows that the agency's attacks on VPNs are consistent with having achieved such a break.

Websites that use one of a few commonly shared 1024-bit Diffie-Hellman groups may be susceptible to passive eavesdropping from an attacker with nation-state resources. Here, we show how various protocols would be affected if a single 1024-bit group were broken in each protocol, assuming a typical up-to-date client (e.g., most recent version of OpenSSH or up-to-date installation of Chrome).

In Common Database Vulnerabilities: Backup Data Exposure I told you the story about a lost backup file that lead to data exposure. I used that story to remind you that you need to protect your backups at least as well as your live data. The lost backup however was not the root cause of the problem. The root cause was flawed key management.

This document contains the most common solutions to IPsec VPN problems. These solutions come directly from service requests that the Cisco Technical Support have solved. Many of these solutions can be implemented prior to the in-depth troubleshooting of an IPsec VPN connection. As a result, this document provides a checklist of common procedures to try before you begin to troubleshoot a connection and call Cisco Technical Support.

Note: Refer to IP Security Troubleshooting - Understanding and Using debug Commands to provide an explanation of common debug commands that are used to troubleshoot IPsec issues on both the Cisco IOS Software and PIX.

This section contains solutions to the most common IPsec VPN problems. Although they are not listed in any particular order, these solutions can be used as a checklist of items to verify or try before you engage in in-depth troubleshooting and call the TAC. All of these solutions come directly from TAC service requests and have resolved numerous customer issues.

In IPsec negotiations, Perfect Forward Secrecy (PFS) ensures that each new cryptographic key is unrelated to any previous key. Either enable or disable PFS on both the tunnel peers; otherwise, the LAN-to-LAN (L2L) IPsec tunnel is not established in the PIX/ASA/IOS router.

The issue occurs because the IPSec VPN negotiates without a hashing algorithm. Packet hashing ensures integrity check for the ESP channel. Therefore, without hashing, malformed packets are accepted undetected by the Cisco ASA and it attempts to decrypt these packets. However, because these packets are malformed, the ASA finds flaws while decrypting the packet. This causes the padding error messages that are seen.

An injection flaw enables a variety of different attack methods. Any application that enables users to update a database, shell command, or operating system call can have an injection flaw. In computing, an interpreter is a program that takes a command, generates an instruction, and performs the action within the application.

Malicious actors use injection flaws to change the commands which leads to new and unintended actions within the application. Leveraging these flaws, attackers can create, read, update, or delete data.

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