diff --git a/ssl/t1_lib.c b/ssl/t1_lib.c
index 86914dc..2fa4101 100644
--- a/ssl/t1_lib.c
+++ b/ssl/t1_lib.c
@@ -296,102 +296,64 @@
 
 char ssl_early_callback_init(struct ssl_early_callback_ctx *ctx)
 	{
-	size_t len = ctx->client_hello_len;
-	const unsigned char *p = ctx->client_hello;
-	CBS extensions;
+	CBS client_hello, session_id, cipher_suites, compression_methods, extensions;
+
+	CBS_init(&client_hello, ctx->client_hello, ctx->client_hello_len);
 
 	/* Skip client version. */
-	if (len < 2)
+	if (!CBS_skip(&client_hello, 2))
 		return 0;
-	len -= 2; p += 2;
 
 	/* Skip client nonce. */
-	if (len < 32)
+	if (!CBS_skip(&client_hello, 32))
 		return 0;
-	len -= 32; p += 32;
 
-	/* Get length of session id. */
-	if (len < 1)
+	/* Extract session_id. */
+	if (!CBS_get_u8_length_prefixed(&client_hello, &session_id))
 		return 0;
-	ctx->session_id_len = *p;
-	p++; len--;
-
-	ctx->session_id = p;
-	if (len < ctx->session_id_len)
-		return 0;
-	p += ctx->session_id_len; len -= ctx->session_id_len;
+	ctx->session_id = CBS_data(&session_id);
+	ctx->session_id_len = CBS_len(&session_id);
 
 	/* Skip past DTLS cookie */
 	if (ctx->ssl->version == DTLS1_VERSION || ctx->ssl->version == DTLS1_BAD_VER)
 		{
-		unsigned cookie_len;
+		CBS cookie;
 
-		if (len < 1)
+		if (!CBS_get_u8_length_prefixed(&client_hello, &cookie))
 			return 0;
-		cookie_len = *p;
-		p++; len--;
-		if (len < cookie_len)
-			return 0;
-		p += cookie_len; len -= cookie_len;
 		}
 
-	/* Skip cipher suites. */
-	if (len < 2)
+	/* Extract cipher_suites. */
+	if (!CBS_get_u16_length_prefixed(&client_hello, &cipher_suites) ||
+		CBS_len(&cipher_suites) < 2 ||
+		(CBS_len(&cipher_suites) & 1) != 0)
 		return 0;
-	n2s(p, ctx->cipher_suites_len);
-	len -= 2;
+	ctx->cipher_suites = CBS_data(&cipher_suites);
+	ctx->cipher_suites_len = CBS_len(&cipher_suites);
 
-	if ((ctx->cipher_suites_len & 1) != 0)
+	/* Extract compression_methods. */
+	if (!CBS_get_u8_length_prefixed(&client_hello, &compression_methods) ||
+		CBS_len(&compression_methods) < 1)
 		return 0;
-
-	ctx->cipher_suites = p;
-	if (len < ctx->cipher_suites_len)
-		return 0;
-	p += ctx->cipher_suites_len; len -= ctx->cipher_suites_len;
-
-	/* Skip compression methods. */
-	if (len < 1)
-		return 0;
-	ctx->compression_methods_len = *p;
-	p++; len--;
-
-	ctx->compression_methods = p;
-	if (len < ctx->compression_methods_len)
-		return 0;
-	p += ctx->compression_methods_len; len -= ctx->compression_methods_len;
+	ctx->compression_methods = CBS_data(&compression_methods);
+	ctx->compression_methods_len = CBS_len(&compression_methods);
 
 	/* If the ClientHello ends here then it's valid, but doesn't have any
 	 * extensions. (E.g. SSLv3.) */
-	if (len == 0)
+	if (CBS_len(&client_hello) == 0)
 		{
 		ctx->extensions = NULL;
 		ctx->extensions_len = 0;
 		return 1;
 		}
 
-	if (len < 2)
+	/* Extract extensions and check it is valid. */
+	if (!CBS_get_u16_length_prefixed(&client_hello, &extensions) ||
+		!tls1_check_duplicate_extensions(&extensions) ||
+		CBS_len(&client_hello) != 0)
 		return 0;
-	n2s(p, ctx->extensions_len);
-	len -= 2;
-
-	if (ctx->extensions_len == 0 && len == 0)
-		{
-		ctx->extensions = NULL;
-		return 1;
-		}
-
-	ctx->extensions = p;
-	if (len != ctx->extensions_len)
-		return 0;
-
-	/* Verify that the extensions have valid lengths and that there are
-	 * no duplicates.
-	 *
-	 * TODO(fork): Port the rest of this processing to CBS.
-	 */
-	CBS_init(&extensions, ctx->extensions, ctx->extensions_len);
-	if (!tls1_check_duplicate_extensions(&extensions))
-		return 0;
+	ctx->extensions = CBS_data(&extensions);
+	ctx->extensions_len = CBS_len(&extensions);
 
 	return 1;
 	}
@@ -402,29 +364,26 @@
 				     const unsigned char **out_data,
 				     size_t *out_len)
 	{
-	size_t len = ctx->extensions_len;
-	const unsigned char *p = ctx->extensions;
+	CBS extensions;
 
-	while (len != 0)
+	CBS_init(&extensions, ctx->extensions, ctx->extensions_len);
+
+	while (CBS_len(&extensions) != 0)
 		{
-		uint16_t ext_type, ext_len;
+		uint16_t type;
+		CBS extension;
 
-		if (len < 4)
+		/* Decode the next extension. */
+		if (!CBS_get_u16(&extensions, &type) ||
+			!CBS_get_u16_length_prefixed(&extensions, &extension))
 			return 0;
-		n2s(p, ext_type);
-		n2s(p, ext_len);
-		len -= 4;
 
-		if (len < ext_len)
-			return 0;
-		if (ext_type == extension_type)
+		if (type == extension_type)
 			{
-			*out_data = p;
-			*out_len = ext_len;
+			*out_data = CBS_data(&extension);
+			*out_len = CBS_len(&extension);
 			return 1;
 			}
-
-		p += ext_len; len -= ext_len;
 		}
 
 	return 0;
diff --git a/ssl/test/bssl_shim.cc b/ssl/test/bssl_shim.cc
index 1dde819..d0117da 100644
--- a/ssl/test/bssl_shim.cc
+++ b/ssl/test/bssl_shim.cc
@@ -16,10 +16,51 @@
 #include <sys/socket.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>
+#include <unistd.h>
 
 #include <openssl/ssl.h>
 #include <openssl/bio.h>
+#include <openssl/bytestring.h>
 
+const char *expected_server_name = NULL;
+int early_callback_called = 0;
+
+int select_certificate_callback(const struct ssl_early_callback_ctx *ctx) {
+  early_callback_called = 1;
+
+  if (expected_server_name) {
+    const unsigned char *extension_data;
+    size_t extension_len;
+    CBS extension, server_name_list, host_name;
+    uint8_t name_type;
+
+    if (!SSL_early_callback_ctx_extension_get(ctx, TLSEXT_TYPE_server_name,
+                                              &extension_data,
+                                              &extension_len)) {
+      fprintf(stderr, "Could not find server_name extension.");
+      return -1;
+    }
+
+    CBS_init(&extension, extension_data, extension_len);
+    if (!CBS_get_u16_length_prefixed(&extension, &server_name_list) ||
+        CBS_len(&extension) != 0 ||
+        !CBS_get_u8(&server_name_list, &name_type) ||
+        name_type != TLSEXT_NAMETYPE_host_name ||
+        !CBS_get_u16_length_prefixed(&server_name_list, &host_name) ||
+        CBS_len(&server_name_list) != 0) {
+      fprintf(stderr, "Could not decode server_name extension.");
+      return -1;
+    }
+
+    if (CBS_len(&host_name) != strlen(expected_server_name) ||
+        memcmp(expected_server_name,
+               CBS_data(&host_name), CBS_len(&host_name)) != 0) {
+      fprintf(stderr, "Server name mismatch.");
+    }
+  }
+
+  return 1;
+}
 
 SSL *setup_test(int is_server) {
   if (!SSL_library_init()) {
@@ -44,6 +85,8 @@
     goto err;
   }
 
+  ssl_ctx->select_certificate_cb = select_certificate_callback;
+
   ssl = SSL_new(ssl_ctx);
   if (ssl == NULL) {
     goto err;
@@ -74,7 +117,6 @@
 
 int main(int argc, char **argv) {
   int i, is_server, ret;
-  const char *expected_server_name = NULL;
 
   if (argc < 2) {
     fprintf(stderr, "Usage: %s (client|server) [flags...]\n", argv[0]);
@@ -153,6 +195,11 @@
               server_name, expected_server_name);
       return 2;
     }
+
+    if (!early_callback_called) {
+      fprintf(stderr, "early callback not called\n");
+      return 2;
+    }
   }
 
   for (;;) {