Argon2
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Argon2 è una derivazione di una chiave crittografica che fu selezionata come vincitrice della competizione sul Password Hashing nel luglio 2015.[1][2] Fu progettata da Alex Biryukov, Daniel Dinu, e Dmitry Khovratovich dall'Università del Lussemburgo.[3] Argon2 è stata rilasciata con licenza Creative Commons CC0 (i.e. pubblico dominio), e fornita in 3 diverse versioni:
- Argon2d
- Argon2i
- Argon2id
Algoritmo
Function Argon2 Inputs: password (P): Bytes (0..232-1) Password (or message) to be hashed salt (S): Bytes (8..232-1) Salt (16 bytes recommended for password hashing) parallelism (p): Number (1..224-1) Degree of parallelism (i.e. number of threads) tagLength (T): Number (4..232-1) Desired number of returned bytes memorySizeKB (m): Number (8p..232-1) Amount of memory (in kibibytes) to use iterations (t): Number (1..232-1) Number of iterations to perform version (v): Number (0x13) The current version is 0x13 (19 decimal) key (K): Bytes (0..232-1) Optional key (Errata: PDF says 0..32 bytes, RFC says 0..232 bytes) associatedData (X): Bytes (0..232-1) Optional arbitrary extra data hashType (y): Number (0=Argon2d, 1=Argon2i, 2=Argon2id) Output: tag: Bytes (tagLength) The resulting generated bytes, tagLength bytes long Generate initial 64-byte block H0. All the input parameters are concatenated and input as a source of additional entropy. Errata: RFC says H0 is 64-bits; PDF says H0 is 64-bytes. Errata: RFC says the Hash is H^, the PDF says it's ℋ (but doesn't document what ℋ is). It's actually Blake2b. Variable length items are prepended with their length as 32-bit little-endian integers. buffer ← parallelism ∥ tagLength ∥ memorySizeKB ∥ iterations ∥ version ∥ hashType ∥ Length(password) ∥ Password ∥ Length(salt) ∥ salt ∥ Length(key) ∥ key ∥ Length(associatedData) ∥ associatedData H0 ← Blake2b(buffer, 64) //default hash size of Blake2b is 64-bytes Calculate number of 1 KB blocks by rounding down memorySizeKB to the nearest multiple of 4*parallelism kilobytes blockCount ← Floor(memorySizeKB, 4*parallelism) Allocate two-dimensional array of 1 KiB blocks (parallelism rows x columnCount columns) columnCount ← blockCount / parallelism; //In the RFC, columnCount is referred to as q Compute the first and second block (i.e. column zero and one ) of each lane (i.e. row) for i ← 0 to parallelism-1 do for each row Bi[0] ← Hash(H0 ∥ 0 ∥ i, 1024) //Generate a 1024-byte digest Bi[1] ← Hash(H0 ∥ 1 ∥ i, 1024) //Generate a 1024-byte digest Compute remaining columns of each lane for i ← 0 to parallelism-1 do //for each row for j ← 2 to columnCount-1 do //for each subsequent column //i' and j' indexes depend if it's Argon2i, Argon2d, or Argon2id (See section 3.4) i′, j′ ← GetBlockIndexes(i, j) Bi[j] = G(Bi[j-1], Bi′[j′]) Further passes when iterations > 1 for nIteration ← 2 to iterations do for i ← 0 to parallelism-1 do for each row for j ← 2 to columnCount-1 do //for each subsequent column //i' and j' indexes depend if it's Argon2i, Argon2d, or Argon2id (See section 3.4) i′, j′ ← GetBlockIndexes(i, j) Bi[0] = G(Bi[columnCount-1], Bi′[j′]) Bi[j] = G(Bi[j-1], Bi′[j′]) Compute final block C as the XOR of the last column of each row C ← B0[columnCount-1] for i ← 1 to parallelism-1 do C ← C xor Bi[columnCount-1] Compute output tag return Hash(C, tagLength)
Funzione di hash a lunghezza variabile
Argon2 fa uso di una funzione di hash capace di produrre digest lunghi fino 232 byte. Questa funzione di hash è costruita internamente su Blake2.
Function Hash(message, digestSize) Inputs: message: Bytes (0..232-1) Message to be hashed digestSize: Integer (1..232) Desired number of bytes to be returned Output: digest: Bytes (digestSize) The resulting generated bytes, digestSize bytes long Hash is a variable-length hash function, built using Blake2b, capable of generating digests up to 232 bytes. If the requested digestSize is 64-bytes or lower, then we use Blake2b directly if (digestSize ≤ 64) then return Blake2b(digestSize ∥ message, digestSize) //concatenate 32-bit little endian digestSize with the message bytes For desired hashes over 64-bytes (e.g. 1024 bytes for Argon2 blocks), we use Blake2b to generate twice the number of needed 64-byte blocks, and then only use 32-bytes from each block Calculate the number of whole blocks (knowing we're only going to use 32-bytes from each) r ← Ceil(digestSize/32)-1; Generate r whole blocks. Initial block is generated from message V1 ← Blake2b(digestSize ∥ message, 64); Subsequent blocks are generated from previous blocks for i ← 2 to r do Vi ← Blake2b(Vi-1, 64) Generate the final (possibly partial) block partialBytesNeeded ← digestSize – 32*r; Vr+1 ← Blake2b(Vr, partialBytesNeeded) Concatenate the first 32-bytes of each block Vi (except the possibly partial last block, which we take the whole thing) Let Ai represent the lower 32-bytes of block Vi return A1 ∥ A2 ∥ ... ∥ Ar ∥ Vr+1
Note
- ^ "Password Hashing Competition"
- ^ Jos Wetzels, Open Sesame: The Password Hashing Competition and Argon2 (PDF), 8 febbraio 2016.
- ^ Argon2: the memory-hard function for password hashing and other applications, Alex Biryukov, et al, October 1, 2015
Collegamenti esterni
- Argon2 source code repository on Github
- (EN) Argon2 specification