The Base64 module isn't available in earlier versions of Ruby 1.9.

Methods
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Class Public methods
decode64(data)

Decodes a base 64 encoded string to its original representation.

ActiveSupport::Base64.decode64("T3JpZ2luYWwgdW5lbmNvZGVkIHN0cmluZw==")
# => "Original unencoded string"

Source: show | on GitHub 

# File activesupport/lib/active_support/base64.rb, line 21
def self.decode64(data)
  data.unpack("m").first
end
encode64(data)

Encodes a string to its base 64 representation. Each 60 characters of output is separated by a newline character.

ActiveSupport::Base64.encode64("Original unencoded string")
# => "T3JpZ2luYWwgdW5lbmNvZGVkIHN0cmluZw==\n"

Source: show | on GitHub 

# File activesupport/lib/active_support/base64.rb, line 13
def self.encode64(data)
  [data].pack("m")
end
strict_encode64(value)

Included in Ruby 1.9

Source: show | on GitHub 

# File activesupport/lib/active_support/base64.rb, line 29
def Base64.strict_encode64(value)
  encode64(value).gsub(/\n/, '')
end