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The $\operatorname{SHA-224}$ is defined in the exact same manner as $\operatorname{SHA-256}$ with different initial values and the digest is obtained truncating the hash value, FIPS PUB 180-4 Page 23. The different initial value provides domain separation. With domain separation $$\operatorname{SHA-224}(m) \neq \operatorname{SHA-256}(m)|_{224}$$ where $|_{... 4 Sponge Construction In sponge construction, the block size$b$has two parts,$r$is the rate and it is the written part and$c$capacity is the untouched part by the input/output,$b= c+r$The output is taken from$r$in the squeezing stage. Therefore not all of the$b\$ is the output. This prevents the length extension attack like in the truncations of ...