crypto: fix unsigned conversion of 4-byte RSA publicExponent #5688

Job	Run time
Build slim tarball	2m 40s
x86_64-darwin: with shared libraries	29m 51s
x86_64-linux: with shared libraries	23m 38s
aarch64-darwin: with shared libraries	22m 17s
aarch64-linux: with shared libraries	19m 16s
	1h 37m 42s

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