I need to transmit some data over the wire and I don't want that data being plain text.
The text I'm sending needs to be reversed so I can't md5/sha256/etc...
What's a good way to encode a salted string?
You're looking for encryption.
What language are you using? You probably have a built-in encryption algorithm you can use.
The idea with hashing is that you can only go one-way.
[plain text]--->(HASH ALGORITHM)--->[hash]
Whereas the idea with encryption is that you can use a key together with some plaintext to create a ciphertext. Then you can use the key on the ciphertext to retrieve the plaintext at any time:
[plain text] + [key] --->(ENCRYPTION ALGORITHM)-->[ciphertext]
[ciphertext] + [key] --->(DECRYPTION ALGORITHM)-->[plain text]
The decryption algorithm for a given encryption algorithm is usually very similar to the encryption algorithm, and it allows for the retrieval of a plaintext message given a ciphertext and the correct key (ie password).
You want to use an encryption function, not a hash - which by definition is one-way.
The AES encryption algorithm would be a good start, as the is probably the most widely used one at present.
You don't want a hash, you want encryption. You should look at Blowfish.
Related
Recently while learning Backend development (Node, Express, MongoDB), I discovered the crypto-js library. According to the docs, we can use the following code to encrypt a message using the AES Encryption -
const ciphertext = CryptoJS.AES.encrypt('my message', 'secret key 123').toString();
However, as I'm new to cryptography, the difference between an encryption algorithm and a secret key is not very clear to me.
I have a message, and I can use the AES encryption algorithm to encrypt/decrypt it. Same way, I can use the AES encryption algorithm to decrypt the message as well. Hence, I don't understand how does a secret key fit in here? How exactly do an encryption algorithm and a secret key work in tandem to secure a message?
I have gone through numerous videos, blogs, StackOverflow posts, etc. on the internet, however, I couldn't understand it completely through all the complex crypto jargon. I do have a faint idea, which I'll describe below with the help of Ceaser's cipher.
In Ceaser's Cipher, what I've understood is that the technique of shifting letters by a certain number (A shifted by 4 places is E) is the encryption algorithm, and the certain number (4) is the secret key.
Can somebody please tell me if I'm correct?
If I'm correct, can you please tell me how exactly this translates in the case of the AES encryption mentioned in the beginning?
If I'm not correct, can anyone explain this with the help of a simple analogy? Please try to minimize the use of crypto jargon, as otherwise I'll get lost again.
The algorithm is a series of steps that happen in processing the data with the secret key to produce the encrypted data.
There are two inputs into the algorithm - the key and the initial data. The algorithm takes those two inputs and produces the encrypted output.
+---------+ +---------+
| Key | | Data |
+---------+ +---------+
\ /
\ /
\ /
\ /
\ /
+-----------+
| Algorithm |
+-----------+
|
+-----------+
| Encrypted |
| Result |
+-----------+
The key and the data are separate from the algorithm. If you change either of them, you will get a different encrypted result without changing the algorithm.
In your example of the very simple Caesar Cipher, the algorithm is that each character in the input is going to be replaced by another character (a substitution cipher) that is offset in the alphabet by some amount.
The key would be what the amount is. So, if the key is 1, then a is replaced by b and b is replaced by c and so on. The code for the algorithm can be written to accept the key as an input parameter or function argument and the algorithm code does not have to be rewritten for a different key. The key is applied to the input data by the algorithm programmatically to produced the result. The same algorithm code works with all the different keys you can pass it.
Can somebody please tell me if I'm correct [in understanding the algorithm and key in the Caesar Cipher]?
Yes, your understanding of that is correct.
If I'm correct, can you please tell me how exactly this translates in the case of the AES encryption mentioned in the beginning?
The AES encryption is a much more complicated algorithm that again accepts input data and a key. In this case, the key is a block of data itself, not just a single number. If you want to know more about how it works, you can find many articles on the web about it so it's probably better to read those than try to repeat all that here. Here's one article: What is AES Encryption and How Does It Work?.
Note, you generally do not need to know how a given encryption algorithm works in order to use it successfully. You do need to know how secure it is, what kind of keys are required, what kind of output it generates and how you decrypt it. But, you don't need to know the details of how the algorithm works. And, you need to select the right type of algorithm (for example, symmetric encryption with the same key used for encryption and description vs. asymmetric encryption such as public key/private key pairs) because this determines how you generate/manage/share secrets.
In your code example:
const ciphertext = CryptoJS.AES.encrypt('my message', 'secret key 123').toString();
CryptoJS.AES.encrypt is a function that implements the algorithm. It accepts two arguments. The first argument is the data you want encrypted. The second argument is a key string where all the data in the key is used in the encryption and the key will need to be supplied again in order to descrypt the data.
The result of the call to CryptoJS.AES.encrypt() is a buffer of data.
I need the algorithm about encrypt and decrypt using RSA algorithm. Now I have public key, private key, and string text. The questions are
I need to know how to encrypt it. Encrypt each character in text or encrypt whole text.
How to decrypt it when ciphertext has only number. How to divide number to decrypt.
p.s. Sorry about my bad English. = ="
The standard way is:
Generate a key of symmetric algorithm (for example, AES).
Encrypt the text with them.
Encrypt this key with RSA using, for example, PKCS#1 notation.
Compose an output structure containing ciphertext, encrypted key and other service information (symmetric algorithm identifier, recipient ID, etc.). Most used format is noted in RFC 5652.
You can take each character from the string take it ascii value encrpyt it and then again convert it into text and store.do it for all characters.This will be your encrypted text.Like wise do it for decryption..
hope it helps
Today I was doing some leisurely reading and stumbled upon Section 5.8 (on page 45) of Recommendation for Pair-Wise Key Establishment Schemes Using Discrete Logarithm Cryptography (Revised) (NIST Special Publication 800-56A). I was very confused by this:
An Approved key derivation function
(KDF) shall be used to derive secret
keying material from a shared secret.
The output from a KDF shall only be
used for secret keying material, such
as a symmetric key used for data
encryption or message integrity, a
secret initialization vector, or a
master key that will be used to
generate other keys (possibly using a
different process). Nonsecret keying
material (such as a non-secret
initialization vector) shall not be
generated using the shared secret.
Now I'm no Alan Turing, but I thought that initialization vectors need not be kept secret. Under what circumstances would one want a "secret initialization vector?"
Thomas Pornin says that IVs are public and he seems well-versed in cryptography. Likewise with caf.
An initialization vector needs not be secret (it is not a key) but it needs not be public either (sender and receiver must know it, but it is not necessary that the Queen of England also knows it).
A typical key establishment protocol will result in both involve parties computing a piece of data which they, but only they, both know. With Diffie-Hellman (or any Elliptic Curve variant thereof), the said shared piece of data has a fixed length and they have no control over its value (they just both get the same seemingly random sequence of bits). In order to use that shared secret for symmetric encryption, they must derive that shared data into a sequence of bits of the appropriate length for whatever symmetric encryption algorithm they are about to use.
In a protocol in which you use a key establishment algorithm to obtain a shared secret between the sender and the receiver, and will use that secret to symmetrically encrypt a message (possibly a very long streamed message), it is possible to use the KDF to produce the key and the IV in one go. This is how it goes in, for instance, SSL: from the shared secret (called "pre-master secret" in the SSL spec) is computed a big block of derived secret data, which is then split into symmetric keys and initialization vectors for both directions of encryption. You could do otherwise, and, for instance, generate random IV and send them along with the encrypted data, instead of using an IV obtained through the KDF (that's how it goes in recent versions of TLS, the successor to SSL). Both strategies are equally valid (TLS uses external random IV because they want a fresh random IV for each "record" -- a packet of data within a TLS connection -- which is why using the KDF was not deemed appropriate anymore).
Well, consider that if two parties have the same cryptographic function, but don't have the same IV, they won't get the same results. So then, it seems like the proposal there is that the two parties get the same shared secret, and each generate, deterministically, an IV (that will be the same) and then they can communicate. That's just how I read it; but I've not actually read the document, and I'm not completely sure that my description is accurate; but it's how I'd start investigating.
IV is public or private, it doesn't matter
let's consider IV is known to attacker, now by looking at encrypted packet/data,
and knowledge of IV and no knowledge on encryption key, can he/she can guess about input data ? (think for a while)
let's go slightly backwards, let's say there is no IV in used in encryption
AES (input, K)= E1
Same input will always produce the same encrypted text.
Attacker can guess Key "K" by looking at encrypted text and some prior knowledge of input data(i.e. initial exchange of some protocols)
So, here is what IV helps. its added with input value , your encrypted text changes even for same input data.
i.e. AES (input, IV, K)= E1
Hence, attacker sees encrypted packets are different (even with same input data) and can't guess easily. (even having IV knowledge)
The starting value of the counter in CTR mode encryption can be thought of as an IV. If you make it secret, you end up with some amount of added security over the security granted by the key length of the cipher you're using. How much extra is hard to say, but not knowing it does increase the work required to figure out how to decrypt a given message.
I'm going to use this kind of approach to store my password:
User enters password
Application salts password with random number
Then with salted password encrypt with some encryption algorithm randomly selected array of data (consisting from predefined table of chars/bytes)
for simplicity it can be used just table of digits, so in case of digits random array would be simply be long enough integer/biginteger.
Then I store in DB salt (modified value) and encrypted array
To check password validity:
Getting given password
Read salt from DB and calculate decrypt key
Try to decrypt encrypted array
If successfull (in mathematical mean) compare decrypted value byte by byte
does it contains only chars/bytes from known table. For instance is it integer/biginteger? If so - password counts as valid
What do you think about this procedure?
In a few words, it's a kind of alternative to using hash functions...
In this approach encryption algorithm is about to be used for calculation of non-inversible value.
EDIT
# Encrypt/decrypt function that works like this:
KEY=HASH(PASSWORD)
CYPHERTEXT = ENCRYPT(PLAINTEXT, KEY)
PLAINTEXT = DECRYPT(CYPHERTEXT, KEY)
# Encrypting the password when entered
KEY=HASH(PASSWORD)+SALT or HASH(PASSWORD+SALT)
ARRAY={A1, A2,... AI}
SOME_TABLE=RANDOM({ARRAY})
ENCRYPTED_TABLE = ENCRYPT(SOME_TABLE, KEY + SALT)
# Checking validity
DECRYPT(ENCRYPTED_TABLE, PASSWORD + SALT) == SOME_TABLE
if(SOME_TABLE contains only {ARRAY} elements) = VALID
else INVALID
From what you write I assume you want to do the following:
# You have some encryption function that works like this
CYPHERTEXT = ENCRYPT(PLAINTEXT, KEY)
PLAINTEXT = DECRYPT(CYPHERTEXT, KEY)
# Encrypting the password when entered
ENCRYPTED_TABLE = ENCRYPT(SOME_TABLE, PASSWORD + SALT)
# Checking validity
DECRYPT(ENCRYPTED_TABLE, PASSWORD + SALT) == SOME_TABLE
First off: No sane person would use such a homemade scheme in a production system. So if you were thinking about actually implementing this in the real world, please go back. Don't even try to write the code yourself, use a proven software library that implements widely accepted algorithms.
Now, if you want to think about it as a mental exercise, you could start off like this:
If you should assume that an attacker will know all the parts of the equation, except the actual password. The attacker, who wants to retrieve the password, will therefore already know the encrypted text, the plaintext AND part of the password.
The chance of success will depend on the actual encryption scheme, and maybe the chaining mode.
I'm not a cryptanalyst myself, but without thinking about it too much I have the feeling that there could be a number of angles of attack.
The proposed scheme is, at best, slightly less secure than simply storing the hash of the password and salt.
This is because the encryption step simply adds a small constant amount of time to checking if each hash value is correct; but at the same time it also introduces classes of equivalent hashes, since there are multiple possible permutations of ARRAY that will be recognised as valid.
You would have to brute force the encryption on every password every time someone logs in.
Read salt from DB and calculate decrypt key
This can't be done unless you know what the password is before hand.
Just salt (And multiple hash) the password.
Best practice is to use unique ivs, but what is unique? Is it unique for each record? or absolutely unique (unique for each field too)?
If it's per field, that sounds awfully complicated, how do you manage the storage of so many ivs if you have 60 fields in each record.
I started an answer a while ago, but suffered a crash that lost what I'd put in. What I said was along the lines of:
It depends...
The key point is that if you ever reuse an IV, you open yourself up to cryptographic attacks that are easier to execute than those when you use a different IV every time. So, for every sequence where you need to start encrypting again, you need a new, unique IV.
You also need to look up cryptographic modes - the Wikipedia has an excellent illustration of why you should not use ECB. CTR mode can be very beneficial.
If you are encrypting each record separately, then you need to create and record one IV for the record. If you are encrypting each field separately, then you need to create and record one IV for each field. Storing the IVs can become a significant overhead, especially if you do field-level encryption.
However, you have to decide whether you need the flexibility of field level encryption. You might - it is unlikely, but there might be advantages to using a single key but different IVs for different fields. OTOH, I strongly suspect that it is overkill, not to mention stressing your IV generator (cryptographic random number generator).
If you can afford to do encryption at a page level instead of the row level (assuming rows are smaller than a page), then you may benefit from using one IV per page.
Erickson wrote:
You could do something clever like generating one random value in each record, and using a hash of the field name and the random value to produce an IV for that field.
However, I think a better approach is to store a structure in the field that collects an algorithm identifier, necessary parameters (like IV) for that parameter, and the ciphertext. This could be stored as a little binary packet, or encoded into some text like Base-85 or Base-64.
And Chris commented:
I am indeed using CBC mode. I thought about an algorithm to do a 1:many so I can store only 1 IV per record. But now I'm considering your idea of storing the IV with the ciphertext. Can you give me more some more advice: I'm using PHP + MySQL, and many of the fields are either varchar or text. I don't have much experience with binary in the database, I thought binary was database-unfriendly so I always base64_encoded when storing binary (like the IV for example).
To which I would add:
IBM DB2 LUW and Informix Dynamic Server both use a Base-64 encoded scheme for the character output of their ENCRYPT_AES() and related functions, storing the encryption scheme, IV and other information as well as the encrypted data.
I think you should look at CTR mode carefully - as I said before. You could create a 64-bit IV from, say, 48-bits of random data plus a 16-bit counter. You could use the counter part as an index into the record (probably in 16 byte chunks - one crypto block for AES).
I'm not familiar with how MySQL stores data at the disk level. However, it is perfectly possible to encrypt the entire record including the representation of NULL (absence of) values.
If you use a single IV for a record, but use a separate CBC encryption for each field, then each field has to be padded to 16 bytes, and you are definitely indulging in 'IV reuse'. I think this is cryptographically unsound. You would be much better off using a single IV for the entire record and either one unit of padding for the record and CBC mode or no padding and CTR mode (since CTR does not require padding - one of its merits; another is that you only use the encryption mode of the cipher for both encrypting and decrypting the data).
Once again, appendix C of NIST pub 800-38 might be helpful. E.g., according to this
you could generate an IV for the CBC mode simply by encrypting a unique nonce with your encryption key. Even simpler if you would use OFB then the IV just needs to be unique.
There is some confusion about what the real requirements are for good IVs in the CBC mode. Therefore, I think it is helpful to look briefly at some of the reasons behind these requirements.
Let's start with reviewing why IVs are even necessary. IVs randomize the ciphertext. If the same message is encrypted twice with the same key then (but different IVs) then the ciphertexts are distinct. An attacker who is given two (equally long) ciphertexts, should not be able to determine whether the two ciphertexts encrypt the same plaintext or two different plaintext. This property is usually called ciphertext indistinguishablility.
Obviously this is an important property for encrypting databases, where many short messages are encrypted.
Next, let's look at what can go wrong if the IVs are predictable. Let's for example take
Ericksons proposal:
"You could do something clever like generating one random value in each record, and using a hash of the field name and the random value to produce an IV for that field."
This is not secure. For simplicity assume that a user Alice has a record in which there
exist only two possible values m1 or m2 for a field F. Let Ra be the random value that was used to encrypt Alice's record. Then the ciphertext for the field F would be
EK(hash(F || Ra) xor m).
The random Ra is also stored in the record, since otherwise it wouldn't be possible to decrypt. An attacker Eve, who would like to learn the value of Alice's record can proceed as follows: First, she finds an existing record where she can add a value chosen by her.
Let Re be the random value used for this record and let F' be the field for which Eve can submit her own value v. Since the record already exists, it is possible to predict the IV for the field F', i.e. it is
hash(F' || Re).
Eve can exploit this by selecting her value v as
v = hash(F' || Re) xor hash(F || Ra) xor m1,
let the database encrypt this value, which is
EK(hash(F || Ra) xor m1)
and then compare the result with Alice's record. If the two result match, then she knows that m1 was the value stored in Alice's record otherwise it will be m2.
You can find variants of this attack by searching for "block-wise adaptive chosen plaintext attack" (e.g. this paper). There is even a variant that worked against TLS.
The attack can be prevented. Possibly by encrypting the random before using putting it into the record, deriving the IV by encrypting the result. But again, probably the simplest thing to do is what NIST already proposes. Generate a unique nonce for every field that you encrypt (this could simply be a counter) encrypt the nonce with your encryption key and use the result as an IV.
Also note, that the attack above is a chosen plaintext attack. Even more damaging attacks are possible if the attacker has the possibility to do chosen ciphertext attacks, i.e. is she can modify your database. Since I don't know how your databases are protected it is hard to make any claims there.
The requirements for IV uniqueness depend on the "mode" in which the cipher is used.
For CBC, the IV should be unpredictable for a given message.
For CTR, the IV has to be unique, period.
For ECB, of course, there is no IV. If a field is short, random identifier that fits in a single block, you can use ECB securely.
I think a good approach is to store a structure in the field that collects an algorithm identifier, necessary parameters (like IV) for that algorithm, and the ciphertext. This could be stored as a little binary packet, or encoded into some text like Base-85 or Base-64.