Bcrypt

bcrypt merupakan fungsi hashing kata sandi yang dirancang oleh dua orang peneliti keamanan komputer Niels Provos dan David Mazières, cipher Blowfish adalah dasar pembuatan bcrypt, dan disajikan di USENIX pada tahun 1999.^[1] bcrypt dapat melindungi dari serangan rainbow table dengan mengunakan salt, selain itu, bcrypt adalah fungsi adaptif: seiring waktu, jumlah iterasi dapat ditingkatkan untuk membuatnya lebih lambat, sehingga tetap aman terhadap serangan pencarian brute-force bahkan dengan meningkatnya daya komputasi.

Fungsi bcrypt merupakan algoritma hash password dasar untuk OpenBSD ^[2] dan sistem lain termasuk beberapa distribusi Linux seperti SUSE Linux .^[3]

bcrypt dapat diimplementasikan pada bahasa pemrograman PHP, Python, JavaScript, C, C ++, C #, Go,^[4] Java,^[5][6] Elixir,^[7] Perl,^[8] Ruby dan bahasa lain

Algortima

Algoritma bcrypt adalah hasil dari enkripsi teks "OrpheanBeholderScryDoubt" 64 kali menggunakan Blowfish . Dalam bcrypt fungsi biasa key setup pada Blowfish digantikan dengan fungsi expensive key setup (EksBlowfishSetup)

Function bcrypt
   Input:
      cost:     Number (4..31)                      log2(Iterations). e.g. 12 ==> 212 = 4,096 iterations
      salt:     array of Bytes (16 bytes)           random salt
      password: array of Bytes (1..72 bytes)        UTF-8 encoded password
   Output: 
      hash:     array of Bytes (24 bytes)

   //Initialize Blowfish state with expensive key setup algorithm
   state  <- EksBlowfishSetup(cost, salt, password)   

   //Repeatedly encrypt the text "OrpheanBeholderScryDoubt" 64 times
   ctext  <- "OrpheanBeholderScryDoubt"  //24 bytes ==> three 64-bit blocks
   repeat (64)
      ctext  EncryptECB(state, ctext) //encrypt using standard Blowfish in ECB mode

   //24-byte <- ctext is resulting password hash
   return Concatenate(cost, salt, ctext)

Expensive key setup

Algoritma bcrypt sangat bergantung pada algoritma key setup "Eksblowfish", berikut algoritmanya:

Function EksBlowfishSetup
   Input:
      cost:     Number (4..31)                      log2(Iterations). e.g. 12 ==> 212 = 4,096 iterations
      salt:     array of Bytes (16 bytes)           random salt
      password: array of Bytes (1..72 bytes)        UTF-8 encoded password
   Output: 
      state:    opaque BlowFish state structure
 
   state  <- InitialState()
   state  <- ExpandKey(state, salt, password)
   repeat (2cost)
      state  <- ExpandKey(state, 0, password)
      state  <- ExpandKey(state, 0, salt)

    return state

Expand key

Berikut algoritma fungsi ExpandKey

Function ExpandKey(state, salt, password)
   Input:
      state:    Opaque BlowFish state structure     Internally contains P-array and S-box entries
      salt:     array of Bytes (16 bytes)           random salt
      password: array of Bytes (1..72 bytes)        UTF-8 encoded password
   Output: 
      state:    opaque BlowFish state structure
 
   //Mix password into the internal P-array of state
   for n  <- 1 to 18 do
      Pn  <- Pn xor password[32(n-1)..32n-1] //treat the password as cyclic

   //Encrypt state using the lower 8 bytes of salt, and store the 8 byte result in P1|P2
   block  <- Encrypt(state, salt[0..63])
   P1  <- block[0..31]  //lower 32-bits
   P2  <- block[32..63] //upper 32-bits

   //Continue encrypting state with salt, and storing results in remaining P-array
   for n  <- 2 to 9 do
      block  <- Encrypt(state, block xor salt[64(n-1)..64n-1]) //encrypt using the current key schedule and treat the salt as cyclic
      P2n-1  <- block[0..31] //lower 32-bits
      P2n  <- block[32..63]  //upper 32-bits

   //Mix encrypted state into the internal S-boxes of state
   for i  <- 1 to 4 do
      for n  <- 0 to 127 do
         block  <- Encrypt(state, block xor salt[64(n-1)..64n-1]) //as above
         Si[2n]    <- block[0..31]  //lower 32-bits
         Si[2n+1]  <- block[32..63]  //upper 32-bits
    return state

Referensi