Ruby hmac sha256 hash differs for variable versus literal

Question

HMAC SHA256 hash generated changes when variable is used in the hashing function than using the literal.

I have to concatenate 4 parameters to generate a message string that is hashed using secret key. The concatenated message string generates a different hash than using the value of message as a literal.

require 'base64'
require 'openssl'

securityKey = 'A93reRTUJHsCuQSHR+L3GxqOJyDmQpCgps102ciuabc='
content = 'hello'
id = '1000000855'
tsp = '1460852115'
guid = '75c6016eaa1e43b4807ba25232797714'

contentmd5 = Base64.encode64(OpenSSL::Digest::MD5.digest(content))
inputString = id + tsp + guid + contentmd5
puts inputString
#Input String is 
#'1000000855146085211575c6016eaa1e43b4807ba25232797714XUFAKrxLKna5cZ2REBfFkg=='

digest = OpenSSL::Digest.new('sha256')
hmac = OpenSSL::HMAC.digest(digest, securityKey, inputString)
securityToken = Base64.encode64(hmac)
puts securityToken
#Hash generated is 7ihOEZNeoJMwjLt84I8WfN5b0VwgYNOg8abPA3nZ0SM=

digest = OpenSSL::Digest.new('sha256')
hmac = OpenSSL::HMAC.digest(digest, securityKey, '1000000855146085211575c6016eaa1e43b4807ba25232797714XUFAKrxLKna5cZ2REBfFkg==')
securityToken = Base64.encode64(hmac)
puts securityToken
#Hash generated is gPNytNGMbhg8b27rklqmEK/9xjNAcOq+7nldzyDL4g0=

KorreyD KorreyD · Accepted Answer · 2016-04-18T16:25:44

looks like Base64.encode64 appends a "\n" to the end of its output so

from docs

encode64(bin) Returns the Base64-encoded version of bin. This method complies with RFC 2045. Line feeds are added to every 60 encoded characters.

this

contentmd5 = Base64.encode64(OpenSSL::Digest::MD5.digest(content))

returns

"XUFAKrxLKna5cZ2REBfFkg==\n"

not

 "XUFAKrxLKna5cZ2REBfFkg=="

--

you can use strict_encode64 to not include line feeds so:

contentmd5 = Base64.strict_encode64(OpenSSL::Digest::MD5.digest(content))

returns

 => "XUFAKrxLKna5cZ2REBfFkg=="

Ruby hmac sha256 hash differs for variable versus literal

1 Answers