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@wishdev
Created Sep 4, 2009
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module BlockTEA
#
# encrypt: Use Corrected Block TEA to encrypt plaintext using password
# Return encrypted text as string
#
def encrypt(plaintext, password)
if plaintext.length == 0
return('') # nothing to encrypt
end
# 'escape' plaintext so chars outside ISO-8859-1 work in single-byte packing, but
# keep spaces as spaces (not '%20') so encrypted text doesn't grow too long, and
# convert result to longs
# v = strToLongs(escape(plaintext).gsub(/%20/,' '))
v = strToLongs(plaintext)
if v.length == 1
v[1] = 0 # algorithm doesn't work for n<2 so fudge by adding nulls
end
k = strToLongs(password.ljust(16).slice(0,16)) # simply convert first 16 chars of password as key
n = v.length
z = v[n-1]
y = v[0]
delta = 0x9E3779B9
#mx, e
sum = 0
(6 + 52.0/n).floor.downto(1) { |q| # 6 + 52/n operations gives between 6 & 32 mixes on each word
sum = (sum + delta) & 0xffffffff
e = sum>>2 & 3
for p in (0...n-1)
y = v[p+1]
mx = ((z>>5 ^ ((y<<2)&0xffffffff)) + (y>>3 ^ ((z<<4)&0xffffffff)) ^ (sum^y) + (k[p&3 ^ e] ^ z)) & 0xffffffff
v[p] = (v[p] + mx) & 0xffffffff
z = v[p]
end
y = v[0]
mx = ((z>>5 ^ ((y<<2)&0xffffffff)) + (y>>3 ^ ((z<<4)&0xffffffff)) ^ (sum^y) + (k[(n-1)&3 ^ e] ^ z)) & 0xffffffff
v[n-1] = (v[n-1] + mx) & 0xffffffff
z = v[n-1]
}
ciphertext = longsToStr(v)
return ciphertext.unpack('a*').pack('m').delete("\n") # base64 encode it without newlines
end
#
# decrypt: Use Corrected Block TEA to decrypt ciphertext using password
#
def decrypt(ciphertext, password)
if ciphertext.length == 0
return('')
end
v = strToLongs(ciphertext.unpack('m').pack("a*")) # base64 decode and convert to array of 'longs'
k = strToLongs(password.ljust(16).slice(0,16))
n = v.length
z = v[n-1]
y = v[0]
delta = 0x9E3779B9
#mx, e
q = (6 + 52.0/n).floor
sum = q*delta
while (sum > 0)
e = sum>>2 & 3
(n-1).downto(1) { |p|
z = v[p-1]
mx = ((z>>5 ^ ((y<<2)&0xffffffff)) + (y>>3 ^ ((z<<4)&0xffffffff)) ^ (sum^y) + (k[p&3 ^ e] ^ z)) & 0xffffffff
v[p] = (v[p] - mx) & 0xffffffff
y = v[p]
}
z = v[n-1]
mx = ((z>>5 ^ ((y<<2)&0xffffffff)) + (y>>3 ^ ((z<<4)&0xffffffff)) ^ (sum^y) + (k[0 ^ e] ^ z)) & 0xffffffff
v[0] = (v[0] - mx) & 0xffffffff
y = v[0]
sum -= delta
end
plaintext = longsToStr(v)
# strip trailing null chars resulting from filling 4-char blocks:
plaintext = plaintext.gsub(/\0+$/,'')
return plaintext
end
# supporting functions
def strToLongs(s)
s << [0,0,0].pack('c*') # Pad with at most three nulls
return s.unpack('L*')
end
def longsToStr(l) # convert array of longs back to string
l.pack('L*')
end
module_function :encrypt, :decrypt, :strToLongs, :longsToStr
end
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