Refactor SHA2 functions and move them to src/common/.

This way both frontend and backends can use them. The functions are taken
from pgcrypto, which now fetches the source files it needs from
src/common/.

A new interface is designed for the SHA2 functions, which allow linking
to either OpenSSL or the in-core stuff taken from KAME as needed.

Michael Paquier, reviewed by Robert Haas.

Discussion: https://www.postgresql.org/message-id/CAB7nPqTGKuTM5jiZriHrNaQeVqp5e_iT3X4BFLWY_HyHxLvySQ%40mail.gmail.com

src/common/sha2_openssl.c

@@ -0,0 +1,102 @@
+/*-------------------------------------------------------------------------
+ *
+ * sha2_openssl.c
+ *	  Set of wrapper routines on top of OpenSSL to support SHA-224
+ *	  SHA-256, SHA-384 and SHA-512 functions.
+ *
+ * This should only be used if code is compiled with OpenSSL support.
+ *
+ * Portions Copyright (c) 2016, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *        src/common/sha2_openssl.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#ifndef FRONTEND
+#include "postgres.h"
+#else
+#include "postgres_fe.h"
+#endif
+
+#include <openssl/sha.h>
+
+#include "common/sha2.h"
+
+
+/* Interface routines for SHA-256 */
+void
+pg_sha256_init(pg_sha256_ctx *ctx)
+{
+	SHA256_Init((SHA256_CTX *) ctx);
+}
+
+void
+pg_sha256_update(pg_sha256_ctx *ctx, const uint8 *data, size_t len)
+{
+	SHA256_Update((SHA256_CTX *) ctx, data, len);
+}
+
+void
+pg_sha256_final(pg_sha256_ctx *ctx, uint8 *dest)
+{
+	SHA256_Final(dest, (SHA256_CTX *) ctx);
+}
+
+/* Interface routines for SHA-512 */
+void
+pg_sha512_init(pg_sha512_ctx *ctx)
+{
+	SHA512_Init((SHA512_CTX *) ctx);
+}
+
+void
+pg_sha512_update(pg_sha512_ctx *ctx, const uint8 *data, size_t len)
+{
+	SHA512_Update((SHA512_CTX *) ctx, data, len);
+}
+
+void
+pg_sha512_final(pg_sha512_ctx *ctx, uint8 *dest)
+{
+	SHA512_Final(dest, (SHA512_CTX *) ctx);
+}
+
+/* Interface routines for SHA-384 */
+void
+pg_sha384_init(pg_sha384_ctx *ctx)
+{
+	SHA384_Init((SHA512_CTX *) ctx);
+}
+
+void
+pg_sha384_update(pg_sha384_ctx *ctx, const uint8 *data, size_t len)
+{
+	SHA384_Update((SHA512_CTX *) ctx, data, len);
+}
+
+void
+pg_sha384_final(pg_sha384_ctx *ctx, uint8 *dest)
+{
+	SHA384_Final(dest, (SHA512_CTX *) ctx);
+}
+
+/* Interface routines for SHA-224 */
+void
+pg_sha224_init(pg_sha224_ctx *ctx)
+{
+	SHA224_Init((SHA256_CTX *) ctx);
+}
+
+void
+pg_sha224_update(pg_sha224_ctx *ctx, const uint8 *data, size_t len)
+{
+	SHA224_Update((SHA256_CTX *) ctx, data, len);
+}
+
+void
+pg_sha224_final(pg_sha224_ctx *ctx, uint8 *dest)
+{
+	SHA224_Final(dest, (SHA256_CTX *) ctx);
+}