crypto: fix unsigned conversion of 4-byte RSA publicExponent #5681

Job	Run time
Build slim tarball	2m 4s
aarch64-linux: with shared libraries	1h 21m 2s
x86_64-darwin: with shared libraries	3h 11m 17s
aarch64-darwin: with shared libraries	1h 49m 10s
x86_64-linux: with shared libraries	1h 49m 23s
	8h 12m 56s

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