# How different is SHA512/224 when compared with SHA512?

From http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf Nist document what i understood is while implementing SHA512 and SHA512/224 the two differences are the Initial hash value and the final result truncation.When i changed the initial hash value of SHA512 to that one of SHA512/224 as specified in the fips 180-4 document and built the CAVS and started testing with the test vector https://pastebin.com/wivUc5eH.

Lets consider the first case:

  Len = 0
Msg = 00
MD = d14a028c2a3a2bc9476102bb288234c415a2b01f828ea62ac5b3e42f


But the result i am obtaining for the above input is:

  SHA512/224 digest
6ed0dd02806fa89e25de060c19d3ac86cabb87d6a0ddd05c333b84f4


Lets consider the second case:

  Len = 8
Msg = 84


But the result i am obtaining for the above input is:

  SHA512/224 digest
8f8fdcb3f617a2d809b3132860b02fee00bdd927d541d42073dd12e7


What am i doing wrong?.Can anyone let me know if the concept i have understood correct.

Your implementation of the algorithms seems to correct, but in the test cases the vectors are those of SHA224. Here are my results:

C:\TMP\0
SHA224: d14a028c2a3a2bc9476102bb288234c415a2b01f828ea62ac5b3e42f
SHA512: cf83e1357eefb8bdf1542850d66d8007d620e4050b5715dc83f4a921d36ce9ce47d0d13c5d85f2b0ff8318d2877eec2f63b931bd47417a81a538327af927da3e
SHA512/224: 6ed0dd02806fa89e25de060c19d3ac86cabb87d6a0ddd05c333b84f4

C:\TMP\8

As stated by FIPS 186-4 (6.6) The only two differences between SHA-512 and SHA-512/224 are the eight 64-bit words used for initialization, given by FIPS 186-4 (5.3.6.1); and result truncation to the first 224 bits of the 512-bit result: $H_0^{(N)}$, $H_1^{(N)}$, $H_2^{(N)}$ each 64-bit, and the high-order 32 bits of $H_3^{(N)}$.