# Significance of rotation constants in SHA-512?

In a single round of SHA-512, in the operations $\Sigma_0(A)$, $\Sigma_1(E)$ why are the constants $28$, $34$, and $39$ used for the number of rotations? What significance do these numbers have? What if they are changed?

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## migrated from security.stackexchange.comJun 8 '14 at 19:27

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You are talking about bit rotations (bit shifts where bits shifted out are shifted in, or rotated back, where a normal bit shift might just introduce zero bits). You cannot change the SHA-512 algorithm by altering these bit shift distances, unless you want to invent a new (not SHA-512) algorithm. – pyramids Jun 8 '14 at 9:16
@pyramids: I think that the question might be more along the lines of "Would this new non-SHA-512 algorithm still have some or all of the general properties of SHA-512? Would different values necessarily compromise collision resistance or pre-image resistance?" Unlike the initial hash or round values, the constants used for bit rotation are not explained in e.g. the wikipedia pseudocode. – Neil Slater Jun 9 '14 at 14:02