A blockchain records data in a sequential log. Haber and Stornetta (1991) proposed this structure for time-stamping the creation of intellectual property, such as a digital document, in order to fix property rights with the creator before it can be copied by others. Haber and Stornetta’s model assured the authenticity of each time stamp using hash functions, a type of cryptography that transforms data into a hexidecimal code of fixed length which cannot be inverted to recover the original input. page 
Blockchains were proposed by Nakamoto (2008) as a method of validating ownership of the virtual currency bitcoin.page
Blockchains were proposed by Nakamoto (2008) as a method of validating ownership of the virtual currency bitcoin.page