What is secret key for JWT based authentication and how to generate it

Question

Recently I started working with JWT based authentication  After user login  a user token is generated which will look like    eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9 eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiYWRtaW4iOnRydWV9 TJVA95OrM7E2cBab30RMHrHDcEfxjoYZgeFONFh7HgQ     It consist of three parts each separated with a dot    First part is header which Base64 encoded  After decoding we will get something like        alg    HS256     Algorithm used    typ    JWT      Second part is claims and Base64 encoded  After decoding we will get something like       sub    1234567890      name    John Doe      admin   true     Third part is signature and is generated with  HMACSHA256      base64UrlEncode header              base64UrlEncode payload        secret base64 encoded          Now what is this secret key and how to generate this secret key    I tried some online generator like  http   kjur github io jsjws tool jwt html  but dint get much help

User · Answer

You can write your own generator  The secret key is essentially a byte array  Make sure that the string that you convert to a byte array is base64 encoded  In Java  you could do something like this  String key    quot random secret key quot   String base64Key   DatatypeConverter printBase64Binary key getBytes     byte   secretBytes   DatatypeConverter parseBase64Binary base64Key

User · Answer

The algorithm  HS256  used to sign the JWT means that the secret is a symmetric key that is known by both the sender and the receiver  It is negotiated and distributed out of band  Hence  if you re the intended recipient of the token  the sender should have provided you with the secret out of band    If you re the sender  you can use an arbitrary string of bytes as the secret  it can be generated or purposely chosen  You have to make sure that you provide the secret to the intended recipient out of band   For the record  the 3 elements in the JWT are not base64-encoded but base64url-encoded  which is a variant of base64 encoding that results in a URL-safe value

User · Answer

What is the secret key does  you may have already known till now  It is basically HMAC SH256  Secure Hash   The Secret is a symmetrical key  Using the same key you can generate   amp  reverify  edit  etc  For more secure  you can go with private  public key  asymmetric way   Private key to create token  public key to verify at client level  Coming to secret key what to give You can give anything   quot sudsif quot    quot sdfn2173 quot   any length you can use online generator  or manually write I prefer using openssl C  Users xyz Desktop gt openssl rand -base64 12 65JymYzDDqqLW8Eg  generate  then encode with base 64 C  Users xyz Desktop gt openssl rand -out openssl-secret txt -hex 20  The generated value is saved inside the file named  quot openssl-secret txt quot  generate   amp  store into a file  One thing is giving 12 will generate  12 characters only  but since it is base 64 encoded  it will be  4 3 n  ceiling value  I recommend reading this article https   auth0 com blog brute-forcing-hs256-is-possible-the-importance-of-using-strong-keys-to-sign-jwts

User · Answer

A Json Web Token made up of three parts  The header  the payload and the signature Now the header is just some metadata about the token itself and the payload is the data that we can encode into the token  any data really that we want  So the more data we want to encode here the bigger the JWT  Anyway  these two parts are just plain text that will get encoded  but not encrypted   So anyone will be able to decode them and to read them  we cannot store any sensitive data in here  But that s not a problem at all because in the third part  so in the signature  is where things really get interesting  The signature is created using the header  the payload  and the secret that is saved on the server   And this whole process is then called signing the Json Web Token  The signing algorithm takes the header  the payload  and the secret to create a unique signature  So only this data plus the secret can create this signature  all right  Then together with the header and the payload  these signature forms the JWT  which then gets sent to the client    Once the server receives a JWT to grant access to a protected route  it needs to verify it in order to determine if the user really is who he claims to be  In other words  it will verify if no one changed the header and the payload data of the token  So again  this verification step will check if no third party actually altered either the header or the payload of the Json Web Token   So  how does this verification actually work  Well  it is actually quite straightforward  Once the JWT is received  the verification will take its header and payload  and together with the secret that is still saved on the server  basically create a test signature    But the original signature that was generated when the JWT was first created is still in the token  right  And that s the key to this verification  Because now all we have to do is to compare the test signature with the original signature  And if the test signature is the same as the original signature  then it means that the payload and the header have not been modified    Because if they had been modified  then the test signature would have to be different  Therefore in this case where there has been no alteration of the data  we can then authenticate the user  And of course  if the two signatures are actually different  well  then it means that someone tampered with the data  Usually by trying to change the payload  But that third party manipulating the payload does of course not have access to the secret  so they cannot sign the JWT  So the original signature will never correspond to the manipulated data  And therefore  the verification will always fail in this case  And that s the key to making this whole system work  It s the magic that makes JWT so simple  but also extremely powerful   Now let s do some practices with nodejs   Configuration file is perfect for storing JWT SECRET data  Using the standard HSA 256 encryption for the signature  the secret should at least be 32 characters long  but the longer the better   config env   JWT SECRET   my-32-character-ultra-secure-and-ultra-long-secret   after 90days JWT will no longer be valid  even the signuter is correct and everything is matched  JWT EXPIRES IN 90   now install JWT using command  npm i jsonwebtoken    Example after user signup passing him JWT token so he can stay logged in and get access of resources   exports signup   catchAsync async  req  res  next    gt      const newUser   await User create       name  req body name      email  req body email      password  req body password      passwordConfirm  req body passwordConfirm          const token   jwt sign   id  newUser  id    process env JWT SECRET        expiresIn  process env JWT EXPIRES IN           res status 201  json       status   success       token      data          newUser                     output     In my opinion  do not take help from a third-party to generate your super-secret key  because you can t say it s secret anymore  Just use your keyboard

User · Answer

What is the secret key The secret key is combined with the header and the payload to create a unique hash  You are only able to verify this hash if you have the secret key  How to generate the key You can choose a good  long password  Or you can generate it from a site like this  Example  but don t use this one now   8Zz5tw0Ionm3XPZZfN0NOml3z9FMfmpgXwovR9fp6ryDIoGRM8EPHAB6iHsc0fb

[jwt] What is secret key for JWT based authentication and how to generate it?

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