diff --git a/Makefile b/Makefile
index 022ac42..f2313c2 100644
--- a/Makefile
+++ b/Makefile
@@ -36,6 +36,7 @@ PREFIX     ?= /usr/local
 includedir  = $(DESTDIR)$(PREFIX)/include
 libdir      = $(DESTDIR)$(PREFIX)/lib
 
+hdrs       += include/bytes.h
 hdrs       += include/haggis.h
 
 srcs       += src/bytes.c
@@ -47,6 +48,8 @@ CFLAGS     += -Wall -Werror
 CFLAGS     += -Iinclude
 CFLAGS     += -fPIC
 
+LIBS       += -lmd
+
 all: libhaggis.a libhaggis.so
 
 %.o: %.c
@@ -56,14 +59,14 @@ libhaggis.a: $(objs)
 	$(AR) rcs $@ $?
 
 libhaggis.so: $(objs)
-	$(CC) -shared -o $@ $?
+	$(CC) -shared -o $@ $? $(LIBS)
 
 install: libhaggis.a libhaggis.so haggis.h
 	[ -d $(includedir) ] || install -d $(includedir)
 	[ -d $(libdir) ] || install -d $(libdir)
 	install -m755 libhaggis.so $(libdir)/
 	install -m644 libhaggis.a $(libdir)/
-	install -m644 $(hdrs) $(includedir)/
+	install -m644 include/haggis.h $(includedir)/
 
 clean:
 	rm -rf *.a *.so src/*.o
diff --git a/include/bytes.h b/include/bytes.h
new file mode 100644
index 0000000..0e58ee8
--- /dev/null
+++ b/include/bytes.h
@@ -0,0 +1,48 @@
+/*                 _,.---._    .-._        .--.-. ,--.--------.         
+ *   _,..---._   ,-.' , -  `. /==/ \  .-._/==/  //==/,  -   , -\
+ * /==/,   -  \ /==/_,  ,  - \|==|, \/ /, |==\ -\\==\.-.  - ,-./        
+ * |==|   _   _\==|   .=.     |==|-  \|  | \==\- \`--`\==\- \
+ * |==|  .=.   |==|_ : ;=:  - |==| ,  | -|  `--`-'     \==\_ \
+ * |==|,|   | -|==| , '='     |==| -   _ |             |==|- |          
+ * |==|  '='   /\==\ -    ,_ /|==|  /\ , |             |==|, |          
+ * |==|-,   _`/  '.='. -   .' /==/, | |- |             /==/ -/          
+ * `-.`.____.'     `--`--''   `--`./  `--`             `--`--`          
+ *                    _ __    ,---.      .-._         .=-.-.  _,.----.   
+ *                 .-`.' ,`..--.'  \    /==/ \  .-._ /==/_ /.' .' -   \
+ *                /==/, -   \==\-/\ \   |==|, \/ /, /==|, |/==/  ,  ,-'  
+ *               |==| _ .=. /==/-|_\ |  |==|-  \|  ||==|  ||==|-   |  .  
+ *               |==| , '=',\==\,   - \ |==| ,  | -||==|- ||==|_   `-' \
+ *               |==|-  '..'/==/ -   ,| |==| -   _ ||==| ,||==|   _  , | 
+ *               |==|,  |  /==/-  /\ - \|==|  /\ , ||==|- |\==\.       / 
+ *               /==/ - |  \==\ _.\=\.-'/==/, | |- |/==/. / `-.`.___.-'  
+ *               `--`---'   `--`        `--`./  `--``--`-`
+ *
+ *	@(#)Copyright (c) 2023, Nathan D. Fisher.
+ *
+ *      This is free software.  It comes with NO WARRANTY.
+ *      Permission to use, modify and distribute this source code
+ *      is granted subject to the following conditions.
+ *      1/ that the above copyright notice and this notice
+ *      are preserved in all copies and that due credit be given
+ *      to the author.
+ *      2/ that any changes to this code are clearly commented
+ *      as such so that the author does not get blamed for bugs
+ *      other than his own.
+*/
+
+#ifndef BYTES_H
+#define BYTES_H
+
+#include <stdint.h>
+#include <stdio.h>
+
+#include "haggis.h"
+
+int load_u16(FILE *stream, union u16 num);
+int store_u16(FILE *stream, union u16 num);
+int load_u32(FILE *stream, union u32 num);
+int store_u32(FILE *stream, union u32 num);
+int load_u64(FILE *stream, union u64 num);
+int store_u64(FILE *stream, union u64 num);
+
+#endif
diff --git a/include/haggis.h b/include/haggis.h
index 9cad369..e131f3e 100644
--- a/include/haggis.h
+++ b/include/haggis.h
@@ -53,13 +53,6 @@ union u64 {
     u8 bytes[8];
 };
 
-int load_u16(FILE *stream, union u16 num);
-int store_u16(FILE *stream, union u16 num);
-int load_u32(FILE *stream, union u32 num);
-int store_u32(FILE *stream, union u32 num);
-int load_u64(FILE *stream, union u64 num);
-int store_u64(FILE *stream, union u64 num);
-
 struct haggis_device {
     union u32 major;
     union u32 minor;
diff --git a/src/bytes.c b/src/bytes.c
index e7b4caa..f1ad7c5 100644
--- a/src/bytes.c
+++ b/src/bytes.c
@@ -34,6 +34,7 @@
 #include <stdio.h>
 #include <stdint.h>
 
+#include "bytes.h"
 #include "haggis.h"
 
 #if __BYTE_ORDER__ == __LITTLE_ENDIAN
diff --git a/src/haggis.c b/src/haggis.c
index 9d07cee..87985a6 100644
--- a/src/haggis.c
+++ b/src/haggis.c
@@ -30,10 +30,14 @@
  *      other than his own.
  */
 
+#include <md5.h>
+#include <sha1.h>
+#include <sha2.h>
 #include <stddef.h>
 #include <stdio.h>
 #include <string.h>
 
+#include "bytes.h"
 #include "haggis.h"
 
 static unsigned char header[7] = {0x89, 'h', 'a', 'g', 'g', 'i', 's'};
@@ -129,8 +133,50 @@ int haggis_load_cksum(FILE *stream, struct haggis_checksum *cksum) {
     return 0;
 }
 
+int validate_md5(struct haggis_file *file) {
+    MD5_CTX ctx;
+    u8 digest[MD5_DIGEST_LENGTH];
+    MD5Init(&ctx);
+    MD5Update(&ctx, *file->data, (size_t)file->len.val);
+    MD5Final(digest, &ctx);
+    if (memcmp(file->cksum->sum->md5, digest, sizeof(digest)))
+        return 2;
+    return 0;
+}
+
+int validate_sha1(struct haggis_file *file) {
+    SHA1_CTX ctx;
+    u8 digest[SHA1_DIGEST_LENGTH];
+    SHA1Init(&ctx);
+    SHA1Update(&ctx, *file->data, (size_t)file->len.val);
+    SHA1Final(digest, &ctx);
+    if (memcmp(file->cksum->sum->sha1, digest, sizeof(digest)))
+        return 2;
+    return 0;
+}
+
+int validate_sha256(struct haggis_file *file) {
+    SHA2_CTX ctx;
+    u8 digest[SHA256_DIGEST_LENGTH];
+    SHA256Init(&ctx);
+    SHA256Update(&ctx, *file->data, (size_t)file->len.val);
+    SHA256Final(digest, &ctx);
+    if (memcmp(file->cksum->sum->sha256, digest, sizeof(digest)))
+        return 2;
+    return 0;
+}
+
 int haggis_validate_cksum(struct haggis_file *file) {
-    // todo
+    switch (file->cksum->tag) {
+    case md5:
+	return validate_md5(file);
+    case sha1:
+	return validate_sha1(file);
+    case sha256:
+	return validate_sha256(file);
+    case skip:
+        return 0;
+    }
     return 0;
 }