diff --git a/src/crypto/asn1.c b/src/crypto/asn1.c
index 47c735c5..9b3864ed 100644
--- a/src/crypto/asn1.c
+++ b/src/crypto/asn1.c
@@ -62,6 +62,10 @@ FILE_LICENCE ( GPL2_OR_LATER );
 	__einfo_error ( EINFO_EINVAL_ASN1_ALGORITHM )
 #define EINFO_EINVAL_ASN1_ALGORITHM \
 	__einfo_uniqify ( EINFO_EINVAL, 0x06, "Invalid algorithm" )
+#define EINVAL_BIT_STRING \
+	__einfo_error ( EINFO_EINVAL_BIT_STRING )
+#define EINFO_EINVAL_BIT_STRING \
+	__einfo_uniqify ( EINFO_EINVAL, 0x07, "Invalid bit string" )
 #define ENOTSUP_ALGORITHM \
 	__einfo_error ( EINFO_ENOTSUP_ALGORITHM )
 #define EINFO_ENOTSUP_ALGORITHM \
@@ -295,7 +299,9 @@ int asn1_shrink_any ( struct asn1_cursor *cursor ) {
  */
 int asn1_boolean ( const struct asn1_cursor *cursor ) {
 	struct asn1_cursor contents;
-	const struct asn1_boolean *boolean;
+	const struct {
+		uint8_t value;
+	} __attribute__ (( packed )) *boolean;
 
 	/* Enter boolean */
 	memcpy ( &contents, cursor, sizeof ( contents ) );
@@ -347,6 +353,87 @@ int asn1_integer ( const struct asn1_cursor *cursor, int *value ) {
 	return 0;
 }
 
+/**
+ * Parse ASN.1 bit string
+ *
+ * @v cursor		ASN.1 cursor
+ * @v bits		Bit string to fill in
+ * @ret rc		Return status code
+ */
+int asn1_bit_string ( const struct asn1_cursor *cursor,
+		      struct asn1_bit_string *bits ) {
+	struct asn1_cursor contents;
+	const struct {
+		uint8_t unused;
+		uint8_t data[0];
+	} __attribute__ (( packed )) *bit_string;
+	size_t len;
+	unsigned int unused;
+	uint8_t unused_mask;
+	const uint8_t *last;
+	int rc;
+
+	/* Enter bit string */
+	memcpy ( &contents, cursor, sizeof ( contents ) );
+	if ( ( rc = asn1_enter ( &contents, ASN1_BIT_STRING ) ) != 0 ) {
+		DBGC ( cursor, "ASN1 %p cannot locate bit string:\n", cursor );
+		DBGC_HDA ( cursor, 0, cursor->data, cursor->len );
+		return rc;
+	}
+
+	/* Validity checks */
+	if ( contents.len < sizeof ( *bit_string ) ) {
+		DBGC ( cursor, "ASN1 %p invalid bit string:\n", cursor );
+		DBGC_HDA ( cursor, 0, cursor->data, cursor->len );
+		return -EINVAL_BIT_STRING;
+	}
+	bit_string = contents.data;
+	len = ( contents.len - offsetof ( typeof ( *bit_string ), data ) );
+	unused = bit_string->unused;
+	unused_mask = ( 0xff >> ( 8 - unused ) );
+	last = ( bit_string->data + len - 1 );
+	if ( ( unused >= 8 ) ||
+	     ( ( unused > 0 ) && ( len == 0 ) ) ||
+	     ( ( *last & unused_mask ) != 0 ) ) {
+		DBGC ( cursor, "ASN1 %p invalid bit string:\n", cursor );
+		DBGC_HDA ( cursor, 0, cursor->data, cursor->len );
+		return -EINVAL_BIT_STRING;
+	}
+
+	/* Populate bit string */
+	bits->data = &bit_string->data;
+	bits->len = len;
+	bits->unused = unused;
+
+	return 0;
+}
+
+/**
+ * Parse ASN.1 bit string that must be an integral number of bytes
+ *
+ * @v cursor		ASN.1 cursor
+ * @v bits		Bit string to fill in
+ * @ret rc		Return status code
+ */
+int asn1_integral_bit_string ( const struct asn1_cursor *cursor,
+			       struct asn1_bit_string *bits ) {
+	int rc;
+
+	/* Parse bit string */
+	if ( ( rc = asn1_bit_string ( cursor, bits ) ) != 0 )
+		return rc;
+
+	/* Check that there are no unused bits at end of string */
+	if ( bits->unused ) {
+		DBGC ( cursor, "ASN1 %p invalid integral bit string:\n",
+		       cursor );
+		DBGC_HDA ( cursor, 0, cursor->data, cursor->len );
+		return -EINVAL_BIT_STRING;
+	}
+
+	return 0;
+}
+
 /**
  * Compare two ASN.1 objects
  *
diff --git a/src/crypto/rsa.c b/src/crypto/rsa.c
index be2696ba..563d6b9b 100644
--- a/src/crypto/rsa.c
+++ b/src/crypto/rsa.c
@@ -241,7 +241,7 @@ static int rsa_parse_integer ( struct rsa_context *context,
  */
 static int rsa_init ( void *ctx, const void *key, size_t key_len ) {
 	struct rsa_context *context = ctx;
-	const struct asn1_bit_string *bit_string;
+	struct asn1_bit_string bits;
 	struct asn1_cursor modulus;
 	struct asn1_cursor exponent;
 	struct asn1_cursor cursor;
@@ -274,17 +274,10 @@ static int rsa_init ( void *ctx, const void *key, size_t key_len ) {
 		asn1_skip ( &cursor, ASN1_SEQUENCE );
 
 		/* Enter subjectPublicKey */
-		asn1_enter ( &cursor, ASN1_BIT_STRING );
-
-		/* Check and skip unused-bits byte of bit string */
-		bit_string = cursor.data;
-		if ( ( cursor.len < sizeof ( *bit_string ) ) ||
-		     ( bit_string->unused != 0 ) ) {
-			rc = -EINVAL;
+		if ( ( rc = asn1_integral_bit_string ( &cursor, &bits ) ) != 0 )
 			goto err_parse;
-		}
-		cursor.data = &bit_string->data;
-		cursor.len -= offsetof ( typeof ( *bit_string ), data );
+		cursor.data = bits.data;
+		cursor.len = bits.len;
 
 		/* Enter RSAPublicKey */
 		asn1_enter ( &cursor, ASN1_SEQUENCE );
diff --git a/src/crypto/x509.c b/src/crypto/x509.c
index f25424a1..dc8745dc 100644
--- a/src/crypto/x509.c
+++ b/src/crypto/x509.c
@@ -54,10 +54,6 @@ FILE_LICENCE ( GPL2_OR_LATER );
 	__einfo_error ( EINFO_EINVAL_ALGORITHM )
 #define EINFO_EINVAL_ALGORITHM \
 	__einfo_uniqify ( EINFO_EINVAL, 0x01, "Invalid algorithm type" )
-#define EINVAL_BIT_STRING \
-	__einfo_error ( EINFO_EINVAL_BIT_STRING )
-#define EINFO_EINVAL_BIT_STRING \
-	__einfo_uniqify ( EINFO_EINVAL, 0x02, "Invalid bit string" )
 #define EINVAL_ALGORITHM_MISMATCH \
 	__einfo_error ( EINFO_EINVAL_ALGORITHM_MISMATCH )
 #define EINFO_EINVAL_ALGORITHM_MISMATCH \
@@ -154,88 +150,6 @@ static uint8_t oid_common_name[] = { ASN1_OID_COMMON_NAME };
 static struct asn1_cursor oid_common_name_cursor =
 	ASN1_OID_CURSOR ( oid_common_name );
 
-/**
- * Parse X.509 certificate bit string
- *
- * @v cert		X.509 certificate
- * @v bits		Bit string to fill in
- * @v raw		ASN.1 cursor
- * @ret rc		Return status code
- */
-static int x509_parse_bit_string ( struct x509_certificate *cert,
-				   struct x509_bit_string *bits,
-				   const struct asn1_cursor *raw ) {
-	struct asn1_cursor cursor;
-	const struct asn1_bit_string *bit_string;
-	size_t len;
-	unsigned int unused;
-	uint8_t unused_mask;
-	const uint8_t *last;
-	int rc;
-
-	/* Enter bit string */
-	memcpy ( &cursor, raw, sizeof ( cursor ) );
-	if ( ( rc = asn1_enter ( &cursor, ASN1_BIT_STRING ) ) != 0 ) {
-		DBGC ( cert, "X509 %p cannot locate bit string:\n", cert );
-		DBGC_HDA ( cert, 0, raw->data, raw->len );
-		return rc;
-	}
-
-	/* Validity checks */
-	if ( cursor.len < sizeof ( *bit_string ) ) {
-		DBGC ( cert, "X509 %p invalid bit string:\n", cert );
-		DBGC_HDA ( cert, 0, raw->data, raw->len );
-		return -EINVAL_BIT_STRING;
-	}
-	bit_string = cursor.data;
-	len = ( cursor.len - offsetof ( typeof ( *bit_string ), data ) );
-	unused = bit_string->unused;
-	unused_mask = ( 0xff >> ( 8 - unused ) );
-	last = ( bit_string->data + len - 1 );
-	if ( ( unused >= 8 ) ||
-	     ( ( unused > 0 ) && ( len == 0 ) ) ||
-	     ( ( *last & unused_mask ) != 0 ) ) {
-		DBGC ( cert, "X509 %p invalid bit string:\n", cert );
-		DBGC_HDA ( cert, 0, raw->data, raw->len );
-		return -EINVAL_BIT_STRING;
-	}
-
-	/* Populate bit string */
-	bits->data = &bit_string->data;
-	bits->len = len;
-	bits->unused = unused;
-
-	return 0;
-}
-
-/**
- * Parse X.509 certificate bit string that must be an integral number of bytes
- *
- * @v cert		X.509 certificate
- * @v bits		Bit string to fill in
- * @v raw		ASN.1 cursor
- * @ret rc		Return status code
- */
-static int x509_parse_integral_bit_string ( struct x509_certificate *cert,
-					    struct x509_bit_string *bits,
-					    const struct asn1_cursor *raw ) {
-	int rc;
-
-	/* Parse bit string */
-	if ( ( rc = x509_parse_bit_string ( cert, bits, raw ) ) != 0 )
-		return rc;
-
-	/* Check that there are no unused bits at end of string */
-	if ( bits->unused ) {
-		DBGC ( cert, "X509 %p invalid integral bit string:\n", cert );
-		DBGC_HDA ( cert, 0, raw->data, raw->len );
-		return -EINVAL_BIT_STRING;
-	}
-
-	return 0;
-}
-
-
 /**
  * Parse X.509 certificate version
  *
@@ -466,7 +380,7 @@ static int x509_parse_public_key ( struct x509_certificate *cert,
 				   const struct asn1_cursor *raw ) {
 	struct x509_public_key *public_key = &cert->subject.public_key;
 	struct asn1_algorithm **algorithm = &public_key->algorithm;
-	struct x509_bit_string *raw_bits = &public_key->raw_bits;
+	struct asn1_bit_string *raw_bits = &public_key->raw_bits;
 	struct asn1_cursor cursor;
 	int rc;
 
@@ -491,8 +405,11 @@ static int x509_parse_public_key ( struct x509_certificate *cert,
 	asn1_skip_any ( &cursor );
 
 	/* Parse bit string */
-	if ( ( rc = x509_parse_bit_string ( cert, raw_bits, &cursor ) ) != 0 )
+	if ( ( rc = asn1_bit_string ( &cursor, raw_bits ) ) != 0 ) {
+		DBGC ( cert, "X509 %p could not parse public key bits: %s\n",
+		       cert, strerror ( rc ) );
 		return rc;
+	}
 
 	return 0;
 }
@@ -569,7 +486,7 @@ static int x509_parse_basic_constraints ( struct x509_certificate *cert,
 static int x509_parse_key_usage ( struct x509_certificate *cert,
 				  const struct asn1_cursor *raw ) {
 	struct x509_key_usage *usage = &cert->extensions.usage;
-	struct x509_bit_string bit_string;
+	struct asn1_bit_string bit_string;
 	const uint8_t *bytes;
 	size_t len;
 	unsigned int i;
@@ -579,8 +496,11 @@ static int x509_parse_key_usage ( struct x509_certificate *cert,
 	usage->present = 1;
 
 	/* Parse bit string */
-	if ( ( rc = x509_parse_bit_string ( cert, &bit_string, raw ) ) != 0 )
+	if ( ( rc = asn1_bit_string ( raw, &bit_string ) ) != 0 ) {
+		DBGC ( cert, "X509 %p could not parse key usage: %s\n",
+		       cert, strerror ( rc ) );
 		return rc;
+	}
 
 	/* Parse key usage bits */
 	bytes = bit_string.data;
@@ -1034,7 +954,7 @@ static int x509_parse ( struct x509_certificate *cert,
 			const struct asn1_cursor *raw ) {
 	struct x509_signature *signature = &cert->signature;
 	struct asn1_algorithm **signature_algorithm = &signature->algorithm;
-	struct x509_bit_string *signature_value = &signature->value;
+	struct asn1_bit_string *signature_value = &signature->value;
 	struct asn1_cursor cursor;
 	int rc;
 
@@ -1062,9 +982,12 @@ static int x509_parse ( struct x509_certificate *cert,
 	asn1_skip_any ( &cursor );
 
 	/* Parse signatureValue */
-	if ( ( rc = x509_parse_integral_bit_string ( cert, signature_value,
-						     &cursor ) ) != 0 )
+	if ( ( rc = asn1_integral_bit_string ( &cursor,
+					       signature_value ) ) != 0 ) {
+		DBGC ( cert, "X509 %p could not parse signature value: %s\n",
+		       cert, strerror ( rc ) );
 		return rc;
+	}
 	DBGC2 ( cert, "X509 %p signatureValue is:\n", cert );
 	DBGC2_HDA ( cert, 0, signature_value->data, signature_value->len );
 
diff --git a/src/include/ipxe/asn1.h b/src/include/ipxe/asn1.h
index cd0d5342..222e32ec 100644
--- a/src/include/ipxe/asn1.h
+++ b/src/include/ipxe/asn1.h
@@ -200,18 +200,14 @@ struct asn1_algorithm {
 /** Declare an ASN.1 OID-identified algorithm */
 #define __asn1_algorithm __table_entry ( ASN1_ALGORITHMS, 01 )
 
-/** An ASN.1 boolean */
-struct asn1_boolean {
-	/** Value */
-	uint8_t value;
-} __attribute__ (( packed ));
-
 /** An ASN.1 bit string */
 struct asn1_bit_string {
-	/** Number of unused bits */
-	uint8_t unused;
 	/** Data */
-	uint8_t data[0];
+	const void *data;
+	/** Length */
+	size_t len;
+	/** Unused bits at end of data */
+	unsigned int unused;
 } __attribute__ (( packed ));
 
 /**
@@ -236,6 +232,10 @@ extern int asn1_skip_any ( struct asn1_cursor *cursor );
 extern int asn1_shrink_any ( struct asn1_cursor *cursor );
 extern int asn1_boolean ( const struct asn1_cursor *cursor );
 extern int asn1_integer ( const struct asn1_cursor *cursor, int *value );
+extern int asn1_bit_string ( const struct asn1_cursor *cursor,
+			     struct asn1_bit_string *bits );
+extern int asn1_integral_bit_string ( const struct asn1_cursor *cursor,
+				      struct asn1_bit_string *bits );
 extern int asn1_compare ( const struct asn1_cursor *cursor1,
 			  const struct asn1_cursor *cursor2 );
 extern int asn1_algorithm ( const struct asn1_cursor *cursor,
diff --git a/src/include/ipxe/x509.h b/src/include/ipxe/x509.h
index a55511b8..8b1dda25 100644
--- a/src/include/ipxe/x509.h
+++ b/src/include/ipxe/x509.h
@@ -16,16 +16,6 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #include <ipxe/refcnt.h>
 #include <ipxe/list.h>
 
-/** An X.509 bit string */
-struct x509_bit_string {
-	/** Data */
-	const void *data;
-	/** Length */
-	size_t len;
-	/** Unused bits at end of data */
-	unsigned int unused;
-};
-
 /** An X.509 serial number */
 struct x509_serial {
 	/** Raw serial number */
@@ -59,7 +49,7 @@ struct x509_public_key {
 	/** Public key algorithm */
 	struct asn1_algorithm *algorithm;
 	/** Raw public key bit string */
-	struct x509_bit_string raw_bits;
+	struct asn1_bit_string raw_bits;
 };
 
 /** An X.509 certificate subject */
@@ -77,7 +67,7 @@ struct x509_signature {
 	/** Signature algorithm */
 	struct asn1_algorithm *algorithm;
 	/** Signature value */
-	struct x509_bit_string value;
+	struct asn1_bit_string value;
 };
 
 /** An X.509 certificate basic constraints set */