I am in need of the "hierarchical" encryption scheme, where there is Master key (MK) and derivative keys (DK) which can be derived from the MK. Ie.
MK => DK1
MK => DK2
MK => DK3.
Strangers can encrypt some message with DK1, DK2 or DK3, and those messages can be decrypted using DK1, DK2 or (and?) DK3. In addition, I want those messages to be decrypted using MK.
Is it possible? Is it reliable? Do I have my head in the clouds?
Regards,
M.
A partial solution. You own the master key, MK and keep it secret. Use that master key as part of the input to a key derivation function(KDF):
KDF(MK, "DK1") => DK1
KDF(MK, "DK2") => DK2
etc.
That will allow you to generate as many derivative keys as you need, each with a different input.
You can pass the DKs to other people without telling them the MK. They can encrypt and decrypt using their own DK. You can recreate their DK whenever you want, since you have the MK and know what the other information you used was.
You won't be able to decrypt their messages directly using the MK, but you will only have the one secret key to store, rather than a lot of them. You can securely delete each DK after you've used it since you can always recreate it as will.
Related
I am trying to understand the usage of SCP DEK in store data command.
As per GP Card spec 2.2.1- "The data encryption key (DEK) for decrypting sensitive data, e.g. secret or private keys. This key is a double length DES key and is used as a static key."
I requirement to encrypt the Store data APDU data. Now I have 3 questions
Is indeed SCP DEK used to encrypt EMV AUKs (Application Unique Keys) present in one of these store data commands?
If statement #1 is correct the which key is used to encrypt data field in the APDU?
Is the an indicator in commands prior to store data which says that data field in store data command would be Encrypted or NOT?
I would be able to set store data CLA, INS, P1 and P2 as per GP card 2.2.1 and Amendment D spec.
Asking this question here since crypto.stackexchange does not have global platform and cryptography tags
Any help is appreciated
Nevermind, I found answer
Yes
S-ENC Secure Channel Protocol '03' – Public Release v1.1.1
section 6.2.6 APDU Command C-MAC and C-DECRYPTION Generation and
Verification
External Authenticate command P1 as per 7.1.2.1 Reference Control Parameter P1 – Security Level - (Encrypted value =03 - C-DECRYPTION and C-MAC/ Clear value = 01 - C-MAC)
I have a application with two users and one middle man, all of them holding the private and public key, To make the secured chat, two users and one middle man are all sending the public key and generate a secured channel. After establishing the channel, the middle man doesn't have the ability to see the encrypted message unless one of the user is sending his own key to the middle man.
i am not very familiar with cryptography, so for this app i know how to encrypt and decrypt the message.
encrypt(data) {
try {
var cipher = Crypto.createCipher('aes-256-cbc', this.password);
var encrypted = Buffer.concat([cipher.update(new Buffer(JSON.stringify(data), "utf8")), cipher.final()]);
FileSystem.writeFileSync(this.filePath, encrypted);
return { message: "Encrypted!" };
} catch (exception) {
throw new Error(exception.message);
}
}
but I don't know how to establish the encrypted channel from the stakeholders' key, and how can the one middle to see the message using his key and one of users' key?
is there a way to accomplish this using the cryptography?
I'm not sure I completely understand, but I think if you want to go with a system that doesn't use public key crypto I would suggest a system using 2 stages of encryption, actually a lot like PGP only both stages use symmetric keys-
1) There is a fixed session key generated by the first person in the chat, this can be a randomly generated number.
2) This session key is then encrypted by the keys belonging to every new member of the chat group and individually sent to them.
3) The new members decrypt with their own unique keys to get the plaintext session key back.
4) This session key is subsequently used to decrypt the messages sent to all participants. The same key can also be used to encrypt and send any new messages from any entitled participant(i.e. has the valid session key) on the chat group.
This is used in some systems but it relies on the unique keys being securely transmitted, in the first instance. If this condition can't be met, it's a problem that can be solved with public key crypto to build an end-to-end secure message system like PGP, whatsapp, etc.
I am using revel to build my webapplication and trying to write authentication module.
I finished with sign up part and now heading to write sign in part.
I read about security part on The definitive guide to form-based website authentication and will use this recommendation.
What I am really do not know is, how sign in works. I am imaging that the process works like this:
User write username and password into the html form and press sign in
Server receive request and the controller will check, if user information match with data on database.
If yes, how continue.
The third point is where I am staying. But I have some idea how could works and not sure, if is the right way.
So when sign in information match with the database, I would set in session object(hash datatype) key value pair signed_in: true. Everytime when the user make a request to the webapplication, that need to be authenticated, I would look in the session object, if signed_in is true or not.
This is the way I would do, but as I mentioned above, I do not know if it is the right way.
Yes like #twotwotwo mentioned, give it the user id and also a role.
So server side rendered flow: Step 1
user sends username (or other identifier) and secret.
using scrypt or bcrypt the secret is checked against the stored salted hash in the database
if it matches you create a struct or a map
serialize struct or map into string (json, msgpack, gob)
encrypt the string with AES https://github.com/gomango/utility/blob/master/crypto.go (for instance). Set a global AES key.
create a unique cookie (or session) identifier (key)
store identifier and raw struct or map in database
send encrypted cookie out (id = encrypted_struct_or_map aka the encrypted string)
On a protected resource (or page): Step 2
read identifier from cookie
check if id exists in db
decode cookie value using AES key
compare values from cookie with stored values
if user.role == "allowed_to_access_this_resource" render page
otherwise http.ResponseWriter.WriteHeader(403) or redirect to login page
Now if you wanted you could also have an application-wide rsa key and before encrypting the cookie value sign the string with the rsa private key (in Step 1). In Step 2 decode with AES key, check if signature valid, then compare content to db stored content.
On any changes you have to update the cookie values (struct/map) and the info in the database.
I'm writing an iPad game that sends hi-score type data (ie data beyond what Game Center supports) to a Google appengine datastore. It sends these updates via http GET or POST requests, such as http://myapp.appspot.com/game/hiscore/925818
Here is how I thought to ensure the appengine datastore isn't spammed with false data.
zip/encrypt the payload data using hardcoded p#ssw0rd saved in the iOS binary. Encode that binary data as base64. Pass base64 payload in the url query string or in the POST data. At handler, unbase64, then unzip data with p#ssw0rd. Follow instructions in payload to update highscore-type data.
CON: If p#ssw0rd is somehow derived from the iOS binary, this scheme can be defeated.
Is this adequate/sufficient? Is there another way to do this?
There is absolutely no way to make sure it's your client that sends the data. All you can try is to obfuscate some thing to make it harder for spammers to submit data.
However I think there are two thing you can do:
Have some kind of secrect key saved in the binary
Have a custom algorithm calculating some checksum
Maybe you can go with a combination of both. Let me give you an example:
Create some custom (complex!) alorithm like (simplyfied):
var result = ((score XOR score / 5) XOR score * 8) BITSHIFT_BY 3
Then use your static stored key with that result and a well known hash function like:
var hash = SHA256(StaticKey + result)
Then send that hash with the score to the server. The server has to "validate" the hash by performing the exact same steps (evaluate algorithm + do the SHA256 stuff) and compare the hashes. If they match the score hopefully comes from your app otherwise throw it away, it comes from a spammer.
However this is only one thing you can do. Have a look at the link from mfanto, there are many other ideas that you can look at.
Be sure to not tell anybody about how you're doing it since this is security through obscurity.
Ok me, there are 2 methods to do this.
1) Purchase an SSL certificate for $FREE.99 and open HTTPS connections only to your server to submit hiscore type data. Connection speed should be around 500 ms due to handshake roundtrip time.
2) Embed an RSA public key certificate in your iOS app, and have the RSA private key on your server.
You can then do 1 of 2 things with this second scheme:
IF your data messages are really small (≤256 B) you can just encrypt and send 256B packages (RSA payload is limited by the number of bits in the key)
ELSE IF the data is too large (>256B), generate a random symmetric key (AES), and pack:
SYMMETRIC AES KEY ENCRYPTED WITH RSA PUBLIC KEY
BINARY DATA ENCODED WITH SYMMETRIC AES KEY
The server then takes the first 256 bytes and decodes it, then the server uses that AES key to decrypt the rest of the message.
The above 2 only prevent eavesdropping, but it means the data format of your messages is hidden. At some level, it is still a type of security by obscurity, since if the hacker has your public key AND your message format, they can manufacture messages.
Looked on google and couldn't find anything.
Any good resources to get started designing my backend for a RESTless webapp thats going to rely heavily on API keys.
I know how to write restless webservices etc, just never used API-keys. Generally do people just generate guids for users etc?
Here's how I'm creating API keys for a web service:
string CreateApiKey(int length)
{
var bytes = new byte[length * 2];
using (var rng = new RNGCryptoServiceProvider())
rng.GetBytes(bytes);
var chars = Convert.ToBase64String(bytes)
.Where(char.IsLetterOrDigit)
.Take(length)
.ToArray();
var key = new String(chars);
return key;
}
GUID's are typically not "random" enough and can be easily guessed by the bad-guys.
Take some "random" data like the user's password hash, some random numbers and run the result through sha1 or a similar hash function.
If you want one API key per account, simply add it to the account metadata table. Otherwise use a table linked to the accountIds to store the api keys.
Server side use a cache using the api-key as the key to store temporarily the account metadata so you only need to go to the db once per session.
And of course everything must go over https to avoid that the API key be stolen.
Now if your service is "session" oriented you can consider using a temporary session key so you do not need to expose the API key. Look for public key encryption to investigate this further.