add support for FIPS 180-4 truncated SHA512 value.

Crypto/Hash/SHA512.hs

@@ -15,6 +15,7 @@ module Crypto.Hash.SHA512
 
 	-- * Incremental hashing Functions
 	, init     -- :: Ctx
+	, init_t   -- :: Int -> Ctx
 	, update   -- :: Ctx -> ByteString -> Ctx
 	, finalize -- :: Ctx -> ByteString
 
@@ -72,6 +73,9 @@ instance Storable Ctx where
 foreign import ccall unsafe "sha512.h sha512_init"
 	c_sha512_init :: Ptr Ctx -> IO ()
 
+foreign import ccall unsafe "sha512.h sha512_init_t"
+	c_sha512_init_t :: Ptr Ctx -> Int -> IO ()
+
 foreign import ccall "sha512.h sha512_update"
 	c_sha512_update :: Ptr Ctx -> CString -> Word32 -> IO ()
 
@@ -97,6 +101,11 @@ finalizeInternalIO ptr =
 init :: Ctx
 init = unsafePerformIO $ allocInternal $ \ptr -> do (c_sha512_init ptr >> peek ptr)
 
+{-# NOINLINE init_t #-}
+-- | init a context using FIPS 180-4 for truncated SHA512
+init_t :: Int -> Ctx
+init_t t = unsafePerformIO $ allocInternal $ \ptr -> do (c_sha512_init_t ptr t >> peek ptr)
+
 {-# NOINLINE update #-}
 -- | update a context with a bytestring
 update :: Ctx -> ByteString -> Ctx

cbits/sha512.c

@@ -193,3 +193,53 @@ void sha512_finalize(struct sha512_ctx *ctx, uint8_t *out)
 	for (i = 0; i < 8; i++)
 		p[i] = cpu_to_be64(ctx->h[i]);
 }
+
+#include <stdio.h>
+
+void sha512_init_t(struct sha512_ctx *ctx, int t)
+{
+	memset(ctx, 0, sizeof(*ctx));
+	if (t >= 512)
+		return;
+
+	switch (t) {
+	case 224:
+		ctx->h[0] = 0x8c3d37c819544da2ULL;
+		ctx->h[1] = 0x73e1996689dcd4d6ULL;
+		ctx->h[2] = 0x1dfab7ae32ff9c82ULL;
+		ctx->h[3] = 0x679dd514582f9fcfULL;
+		ctx->h[4] = 0x0f6d2b697bd44da8ULL;
+		ctx->h[5] = 0x77e36f7304c48942ULL;
+		ctx->h[6] = 0x3f9d85a86a1d36c8ULL;
+		ctx->h[7] = 0x1112e6ad91d692a1ULL;
+		break;
+	case 256:
+		ctx->h[0] = 0x22312194fc2bf72cULL;
+		ctx->h[1] = 0x9f555fa3c84c64c2ULL;
+		ctx->h[2] = 0x2393b86b6f53b151ULL;
+		ctx->h[3] = 0x963877195940eabdULL;
+		ctx->h[4] = 0x96283ee2a88effe3ULL;
+		ctx->h[5] = 0xbe5e1e2553863992ULL;
+		ctx->h[6] = 0x2b0199fc2c85b8aaULL;
+		ctx->h[7] = 0x0eb72ddc81c52ca2ULL;
+		break;
+	default: {
+		char buf[8+4];
+		uint8_t out[64];
+		int i;
+
+		sha512_init(ctx);
+		for (i = 0; i < 8; i++)
+			ctx->h[i] ^= 0xa5a5a5a5a5a5a5a5ULL;
+
+		i = sprintf(buf, "SHA-512/%d", t);
+		sha512_update(ctx, buf, i);
+		sha512_finalize(ctx, out);
+
+		/* re-init the context, otherwise len is changed */
+		memset(ctx, 0, sizeof(*ctx));
+		for (i = 0; i < 8; i++)
+			ctx->h[i] = cpu_to_be64(((uint64_t *) out)[i]);
+		}
+	}
+}

cbits/sha512.h

@@ -49,4 +49,6 @@ void sha512_init(struct sha512_ctx *ctx);
 void sha512_update(struct sha512_ctx *ctx, uint8_t *data, uint32_t len);
 void sha512_finalize(struct sha512_ctx *ctx, uint8_t *out);
 
+void sha512_init_t(struct sha512_ctx *ctx, int t);
+
 #endif