+New applications should use the SHA2 digest algorithms such as SHA256.
+The other digest algorithms are still in common use.
+
+For most applications the B<impl> parameter to EVP_DigestInit_ex() will be
+set to NULL to use the default digest implementation.
+
+The functions EVP_DigestInit(), EVP_DigestFinal() and EVP_MD_CTX_copy() are
+obsolete but are retained to maintain compatibility with existing code. New
+applications should use EVP_DigestInit_ex(), EVP_DigestFinal_ex() and
+EVP_MD_CTX_copy_ex() because they can efficiently reuse a digest context
+instead of initializing and cleaning it up on each call and allow non default
+implementations of digests to be specified.
+
+In OpenSSL 0.9.7 and later if digest contexts are not cleaned up after use
+memory leaks will occur.
+
+Stack allocation of EVP_MD_CTX structures is common, for example:
+
+ EVP_MD_CTX mctx;
+ EVP_MD_CTX_init(&mctx);
+
+This will cause binary compatibility issues if the size of EVP_MD_CTX
+structure changes (this will only happen with a major release of OpenSSL).
+Applications wishing to avoid this should use EVP_MD_CTX_create() instead:
+
+ EVP_MD_CTX *mctx;
+ mctx = EVP_MD_CTX_create();
+