def pkcs_emsa_pss_encode(M, emBits, h, mgf, sLen):
"""
Implements EMSA-PSS-ENCODE() function described in Sect. 9.1.1 of RFC 3447
Input:
M : message to be encoded, an octet string
emBits: maximal bit length of the integer resulting of pkcs_os2ip(EM),
where EM is the encoded message, output of the function.
h : hash function name (in 'md2', 'md4', 'md5', 'sha1', 'tls',
'sha256', 'sha384'). hLen denotes the length in octets of
the hash function output.
mgf : the mask generation function f : seed, maskLen -> mask
sLen : intended length in octets of the salt
Output:
encoded message, an octet string of length emLen = ceil(emBits/8)
On error, None is returned.
"""
# 1) is not done
hLen = _hashFuncParams[h][0] # 2)
hFunc = _hashFuncParams[h][1]
mHash = hFunc(M)
emLen = int(math.ceil(emBits/8.))
if emLen < hLen + sLen + 2: # 3)
warning("encoding error (emLen < hLen + sLen + 2)")
return None
salt = randstring(sLen) # 4)
MPrime = '\x00'*8 + mHash + salt # 5)
H = hFunc(MPrime) # 6)
PS = '\x00'*(emLen - sLen - hLen - 2) # 7)
DB = PS + '\x01' + salt # 8)
dbMask = mgf(H, emLen - hLen - 1) # 9)
maskedDB = strxor(DB, dbMask) # 10)
l = (8*emLen - emBits)/8 # 11)
rem = 8*emLen - emBits - 8*l # additionnal bits
andMask = l*'\x00'
if rem:
j = chr(reduce(lambda x,y: x+y, map(lambda x: 1<<x, range(8-rem))))
andMask += j
l += 1
maskedDB = strand(maskedDB[:l], andMask) + maskedDB[l:]
EM = maskedDB + H + '\xbc' # 12)
return EM # 13)
评论列表
文章目录
