openssl默認使用的是PEM格式，經過base64。
生成pem格式的私鑰：
openssl genrsa -out private_key.pem 1024
生成公鑰：
openssl rsa -in private_key.pem -pubout -out public_key.pem
產生的密鑰如下：
[wind@localhostkey]$cat private_key.pem -----BEGINRSAPRIVATEKEY-----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-----ENDRSAPRIVATEKEY-----[wind@localhostkey]$[wind@localhostkey]$[wind@localhostkey]$openssl rsa -inprivate_key.pem -pubout -out public_key.pemwritingRSAkey[wind@localhostkey]$cat public_key.pem -----BEGINPUBLICKEY-----MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCd3V5+GjpOwqNks9ProDGaZT2qURAAuAodHcUM3P1mnhOh4l4uVdvkXunUI7K6XDg6Xu9eL1WDQc6qKXs/OD91LS+RpkIAb2gMU8hGrNfR34izZh36KdfWnEQpniAiFsHsg2ddAaPtGZZ8/jpjuPq32IVZJkgyKcWqnz5aL3FMXQIDAQAB-----ENDPUBLICKEY-----
某些語言需要pkcs8格式的公鑰。 （php就不需要了）
使用openssl將剛才生成的公鑰轉為pkcs#8格式：
openssl pkcs8 -topk8 -inform PEM -in private_key.pem -outform PEM -nocrypt -out private_key_pkcs8.pem
