I'm using an OpenSSL cipher in Ruby to send text between a client and server and apparently it's a good idea to employ an IV, but for decryption on the server-side, I'm going to need that IV which was generated client-side. My question is will I run into problems sending the IV over the network? I don't know the first thing about cryptography, so I have no idea whether the IV can be used to decrypt the message or not.
The IV is public information, it's totally fine to send it over the network. However, you should use a cryptographically secure random for every single encryption, especially if you are using CBC mode. Using a somehow predictable IV in a situation like that leaves your encryption vulnerable to certain kinds of attacks.
If you are completely new to cryptography and using Cipher, have a look at the docs, we added some information there that should help you getting started. It illustrates some best practices, among them is handling the IV correctly.
The IV ensures that even if you were to encrypt two identical plaintexts using the same key, they produce distinct ciphertexts (because a new, randomly generated IV should be used for every encryption).
The IV cannot be used to decrypt the message without the key, and does not need to be transmitted securely, so it can be safely sent over the network along with the encrypted message.
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everyone. I'm learning Laravel and I'm in the start of my journey. I was learning about encryption and decryption in Laravel today and then this thought came into my mind. Could be a stupid one but I want to know my answers.
Let's say I make a database which stores sensitive information about users and I encrypt all the data before storing into the database, let's just say using the Encrypt class of Laravel. Now my questions:
If someone steals that database and luckily finds out that this information was encrypted using techniques provided by Laravel or any other technique. Can't that person descript that all data using the same decryption technique that was used to encrypt it. If this can be done, then what's the point of doing this encryption?
If that can be done then how can we make sure that our data is actually encrypted and is safe even if someone steals it?
Thank you guys!
I encrypted my data and then decrypted it and want my answer that how that encrypted data is even safe.
You might want to read up on the basics of encryption.
The common approach is that the technique by which you encrypt should be as open as possible - because the more people look at the algorithm, the less likely there might be bugs.
However, even if the algorithm is public, the key is not. Only people who have the key can decrypt properly encrypted data. This is true of the AES algorithm Laravel uses too.
The mathematics are complicated, but essentially the length of the key determines the amount of computer resources required to break the encryption.
THe real-world example is that everyone knows how door locks work. There are millions of locks that all work in the same way - but only people who have a key can open the door.
So, if an attacker steals your database, they cannot read your content unless they also have the key, as long as the key length is sufficient.
If someone steals that database and luckily finds out that this information was encrypted using techniques provided by Laravel or any other technique. Can't that person descript that all data using the same decryption technique that was used to encrypt it. If this can be done, then what's the point of doing this encryption?
If someone steals that database they will still need a decryption key to decrypt (thats why strong passwords are recommended) so even if they bruteforce it will become almost impossible to decrypt.
The way you’re asking if encrypt and decrypt is easy then i think you’re asking some encryption like base64.
With AES bruteforcing their way in becomes difficult. In laravel encrypt or crypt class it uses AES-256-CBC which is pretty good at that.
Then there is Hash library they are one way encryption techniques which uses bcrypt it can only be verified and not decrypt you have to run all combinations for lines everytime to brute force. Unlike md5 which gives same encryted string every time.
I use a code who do AES encoding, and I use it for more than 10 years. The problem i don't know if this code is well written or not! The algorithm was written more than 15 years ago, is very tiny (only one hundred of lines) and can compile on ios/android/windows 32bit-64bit/MacOs.
For example in the code i saw that :
The password is hashed with MD5 (so in 16 bytes) before to be send to the encryption algorithm. I can of course change this part easily but what other algorithm to use ? SHA2 ?
The iV is initialized with current time, and then the first block of the compression output is the iV (so it's public). Don't know if it's good or bad !
What else i need to check ?
Now how can i check the validity of the output to know if everything work as expected ?
use a code who do AES encoding, and I use it for more than 10 years. The problem i don't know if this code is well written or not!
It is called encryption. And from the question ( ~ 100 lines) I assume you'd like to validate a code which is using AES encryption, not the AES encryption itself. I wrote a small blog about encryption. It is focused on Java, but principles are universal
The password is hashed with MD5 (so in 16 bytes) before to be send to the encryption algorithm. I can of course change this part easily but what other algorithm to use ? SHA2 ?
Do you mean - hash of the password is used as an encryption key? (I see that often)
If that's the case, it may be not sufficient today. If the passwords are human-provided (not long random data with high entropy), it's better to use some PBKDF to generate an encryption key from a password.
The iV is initialized with current time, and then the first block of the compression output is the iV (so it's public). Don't know if it's good or bad !
IV needs to be unique and may be public. Some encryption modes (e.g. CBC) requires IV to be unpredictable (random)
What else i need to check ?
You may check if the AES implementation itself is provided by some mature library/framework to prevent some side-channel attacks.
As well data should be authenticated (signed, appended hash, ..) to prevent maleability (it is called authenticated encryption)
Now how can i check the validity of the output to know if everything work as expected ?
well - it's only you who can tell of the output is correct or not.
I have a very large block of code (few seconds to crypt).
I use KeyA to encrypt it.
later in the process, i receive a key (not necessarily KeyA)...
but i don't need to open the block yet,
what i really need, is to validate that this is really the Key that will open the code correctly.
I Assumed i can keep a known block, and encrypt it,
and in order to validate the key, only open it, but it feels like weakenning the power of the cryptography (brute-force is easier, one can learn few things about the key properties).
Does my assumption really weakening the chipher? why yes/why no?
Is there a different way to ensure the match of a key without opening the whole block.
I am assuming you are using Symmetric-Key Cryptography (the kind where the key used to decrypt the file is the same as the one used to encrypt it).
If the cipher is vulnerable to a Known-Plaintext Attack, then the known block of plaintext may reveal information about the key. The stream cipher used for ZIP files suffered from this problem. Because ZIPs are compressed, it was difficult to guess enough plain-text, but the checksum used to verify passwords (among other factors) helped provide sufficient plain-text for a practical attack.
In principle you could publicize the hash of KeyA (assuming that the hash algorithm is strong enough that it cannot be reversed, and that the hash algorithm isn't also used internally by the cipher). This would allow you to quickly reject invalid keys without changing the way the message is encrypted.
Taking this idea further, you could use a Message authentication code such as HMAC. A message authentication code will validate that the message (in this case your very large block of code, or perhaps just its file path) has not been tampered with, as well as validating that the key is correct.
If you are concerned that this will make brute force easier or expose properties of the key, you could split the key into two parts. The first part of the key could be purely for validation, and the second part purely for decryption. e.g. MyKey = AuthenticationPart,DecryptionPart
(Disclaimer: This is based on my very incomplete understanding of crypto. You might get better responses from the experts on security.stackexchange.com and/or crypto.stackexchange.com)
I need to write a simplified encryption API that can easily deal with symmetric encryption, either by using a random generated key or a password-derived key.
The password generation is performed with the PKCS5_PBKDF2_HMAC() function from the OpenSSL library and using EVP_sha256() as hashing algorithm and a random generated 16-byte salt.
The symmetric encryption is performed with the OpenSSL EVP API.
My question is: how (in)secure is it to use the password derivation salt also as the IV for encryption?
The reason behind this question is that this will allow me to simplify the API and the output stream in the following way:
for the encryption routine, a user would have to provide either the password or the secret key; based on whichever is provided, the code can decide if a key needs to be derived from the password or use the provided key as it is;
similarly, for the decryption routine, a user would have to provide either the password or the secret key; based on whichever is provided, the key could be re-derived from the password and the IV, which is also acting as a password salt (and is put first in the output stream, right before the ciphertext);
the output stream will consist only of the IV concatenated with the ciphertext, eliminating a separate salt;
the output stream will be the same for a random generated key or a password-derived key.
Note: the API automatically takes care of the salt/IV generation, which is randomly generated for each encryption session, so even if a password is reused, the key is guaranteed to be different.
Thank you in advance for your answers.
As it happens, I've run into pretty much exactly the same scenario while working on one of my own projects (where a message is encrypted in CBC-mode with a random IV, and the user can either specify a key or a textual password).
Similar questions are discused here and here. To summarize: the purpose of an IV is to ensure that ciphertext remains unique even if the key is reused. As long as you're generating a new IV per message like you said you are, the source of the key doesn't matter as much. Which means you're probably safe reusing the salt as the IV, as far as anyone knows right now. It doesn't even seem like it would even make sense for it to be an issue, because the salt gets put through a cryptographic hash before deriving the key in a different way; as long as you use a good hashing function in PBKDF2 (i.e. SHA-256 as mentioned above), a key so derived is indistinguishable from one which was randomly generated, which in this case it might have been.
However, people uncover unexpected things in the world of cryptanalysis all the time, and straight-up reusing the same data in two places is considered A Bad Thing in principle even if we don't know of any practical problems right this minute. Should you actually be worried about this? At my level of knowledge on cryptanalysis, I'm somewhere between "maybe" and "I don't know," which is a little too much uncertainty for my tastes, so I'm going with the "technically safer" course of action, which is generating separate IV and salt values. Transmitting both the salt and the IV is a perfectly cromulent security practice, and you have nothing to lose if the user directly inputs the key and the salt goes unused.
I'm developing an application that on one side produces a code with certain information about a purchase, wich includes a credit information. For example, you could buy a given number of minutes to spend in a public PC on a cybercafe, and you receive a ticket with a number/code with that ammount of minutes, which is then decoded and processed by the PC blocking software in the public PC.
The full length of that information (including date of purchase, an ID, and so on) is about 12 bytes. I need to secure that data, obviously, as much as i need to make it unalterable.
I don't have experience on cryptography but have been reading a lot the last few days, so i came up with an scheme in which i encrypt the data using Twofish in CFB mode (to keep the ciphertext small), and add a 4 bytes long IV, randomly generated. I realize it's a short IV, but the reasoning behind is that an attacker should grab an apparently ridiculous ammount of tickets to become a thread with an IV of 65535 variations.
The problem i see (let alone the ones i miss) is that i also need to authenticate the code, since in CFB mode, a small change in the ciphertext produces just a small change in the plaintext, so anybody could change, for instance, its ticket's credit by just changing an A for a B.
So, first question is: is there any obvious problem in using the CRC16 of the plaintext as IV, and add it (unencrypted) to the encrypted code to use it both for authentication and IV? I repeat i'm not in cryptography, but it 'feels' odd to put some information about the plaintext unencrypted along with the cyphertext. But is just the gut feeling.
Or, instead, should i use a stream cipher? Which one could make a big change (/mess up) the plaintext from a small change in ciphertext. Is this related to the error propagation property in the cipher mode of operation?
Some guide, please?
Thanks a lot.
By the way, if that matters, im using mcrypt on PHP.
I must add that the other end of the app, the one that reads the ticket, is not (and cannot be) online. Sorry for that ommision.
It sounds like what you are looking for is either an HMAC or, if you cannot secure the client PCs, a digital signature, not encryption.
I would add some salt and produce an MD5 hash, delivered right with the plaintext