Mask generation function: Difference between revisions

Revision as of 10:08, 27 June 2023

Latest revision as of 20:03, 8 April 2024

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Line 69:

hLen = hash_func().digest_size

# https://www.ietf.org/rfc/rfc2437.txt

# 1. If l > 2^32(hLen), output "mask too long" and stop.

if length > (hLen << 32):

raise ValueError("mask too long")

# 2. Let T be the empty octet string.

T = b""

# 3. For counter from 0 to \lceil{l / hLen}\rceil-1, do the following:

# Note: \lceil{l / hLen}\rceil-1 is the number of iterations needed,

# but it's easier to check if we have reached the desired length.

counter = 0

while len(T) < length:

# a. Convert counter to an octet string C of length 4 with the primitive I2OSP: C = I2OSP (counter, 4)

C = int.to_bytes(counter, 4, '"big'")

# b. Concatenate the hash of the seed Z and C to the octet string T: T = T || Hash (Z || C)

T += hash_func(seed + C).digest()

counter += 1

# 4. Output the leading l octets of T as the octet string mask.

return T[:length]

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