erlang java 加解密（2）消息摘要算法（MD、SHA、MAC）之SHA
java加解密相关资料和代码参考《java加密与解密的艺》http://snowolf.iteye.com/blog/379860
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sha(Data) -> DigestTypes:Data = iolist() | binary()Digest = binary()Computes an SHA message digest from Data, where the length of the digest is 160 bits (20 bytes).计算Data的SHA消息摘要。摘要的长度是160位（20字节）。sha_init() -> ContextTypes: Context = binary()Creates an SHA context, to be used in subsequent calls to sha_update/2.创建SHA的context 用于之后的sha_update/2sha_update(Context, Data) -> NewContextTypes: Data = iolist() | binary()Context = NewContext = binary()Updates an SHA Context with Data, and returns a NewContext.用Data更新一个SHA的context 返回NewContextsha_final(Context) -> DigestTypes: Context = Digest = binary()Finishes the update of an SHA Context and returns the computed SHA message digest.完成SHA Context的更新 ，返回SHA信息摘要
