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)
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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.
There are many operating system and programs that hash passwords for authentication.
Even though they can encrypt the password in many different ways and save it
why do they save the hash of them?
Is the only reason to that question that encrypting them may cause in breaking and decrypting them or there are other reasons?
Thanks for answering in advance
User credentials (≈passwords) are among the most valuable assets stored in an application. They are a prime target for attackers, and as a developer, you want to protect them the best you can.
The principle of defense in depth (and common sense) indicates that the more layers of protection you can put around something, the more secure it will be. So as you also mentioned, the purpose of hashing passwords is that even if there is a breach, an attacker still can't get hold of actual user credentials.
The problem with encryption is always key management. If passwords were stored encrypted, they would need to be decrypted (or the received password encrypted with the same key) to be able to verify a password. For this, the application would need to have access to the key. But that negates the purpose of encryption, an attacker would also have access to the key in case of a breach. (Public key cryptography could make it somewhat more difficult, but essentially the same problem of key management would still persist.)
So in short, only storing salted hashes with an algorithm that is slow enough to prevent brute-force attacks (like PBKDF2 or Bcrypt) is both the simplest and the most secure. (Also note that plain salted hashes are not good enough anymore.)
Think of the need: You define your new password, and then every time you log-in the entered password is hashed and checked against the stored value. This is the simplest and most secure policy to handle this (since no one will be able to re-construct your password from the stored value). Moreover, imagine that you use the same password in several systems. If Windows would enable (regardless how hard it would be) to re-construct your password from what is stored in a Windows system, there would be (quite many) people that would blame Microsoft for security breach on other system (which could derivate into legal actions).
To summarize, simplicity and commercially logical approach.
Well, actually it's for security reason.
Hash functions are usually not revertibles, so even if someone finds out the hashes it would be really difficult for him to find which password generated that hash value.
Obviously you can try with a dictionary attack or a brute force one, trying to find out the password which generated the hash but it could take a very long time.
Consider that you have a Database with user and their passowrd, take note that a lot of people use the very same password everywhere.
Now immagine if a cracker manages to crack into your DB and finds all the password written clearly. That would be a disaster.
To start, I am trying to encrypt very sensitive information on a public website. Users will be able to update their information, Administrators will need access to this information. I am worried that if the encrypted data is some how compromised, then everyone's information would be as well due to them all using the same salt and key.
So I know using a salt, and key is always preferred. But as mentioned above if they reverse engineer the encrypted data, what use it is.
My solution, is to have the key and salt stored in a DB, with many rows and columns, any of which can be used for the salt or key. I would have an algorithm that will use "something" fixed in the users account that will be used to figure out which salt and key to use. This way statistically speaking no 2 years will have same combo of salt and key.
Is this over kill, or good?
I question the value of this second database that holds keys and salts. Consider:
The "something" in the user's data that identifies the salt and key will necessarily have to be encrypted differently from the rest of the user's data. Otherwise, you wouldn't be able to get it without first already having it.
Statistical analysis of the encrypted user data would almost certainly discover that the "something" is encrypted differently. That will be like waving a red flag at a bull, and an attacker will concentrate on figuring out why that's different.
You can assume that if an attacker can get the database of encrypted user information, he can also get the database of salts and keys.
Given that, there are two possible scenarios:
The encryption of the "something" that identifies the key and salt is unbreakable. That is, it's so good that the attacker's best efforts fail to reveal the connection between that "something" and the key/salt database.
The attacker discovers the encryption of the "something," and therefore is able to decrypt your sensitive data.
If #1 is the case, then you probably should use that encryption algorithm for all of your user data. Why do something in two steps when you can do it just as effectively in one?
If #2 is the case, then all the work you've done just put up a little bump in the road for the attacker.
So, short answer: what you propose looks like either unnecessary work or ineffective road blocking. In either case, it looks to me like a whole lot of work and added complexity for no appreciable gain.
That said, I could have misinterpreted your brief description. If so, please correct me.
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