diff --git a/include/polarssl/oid.h b/include/polarssl/oid.h
index 025a15f..b0e781f 100644
--- a/include/polarssl/oid.h
+++ b/include/polarssl/oid.h
@@ -409,11 +409,12 @@
  * \param md_alg   message digest algorithm
  * \param pk_alg   public key algorithm
  * \param oid      place to store ASN.1 OID string pointer
+ * \param olen     length of the OID
  *
  * \return         0 if successful, or POLARSSL_ERR_OID_NOT_FOUND
  */
 int oid_get_oid_by_sig_alg( pk_type_t pk_alg, md_type_t md_alg,
-                            const char **oid_str );
+                            const char **oid, size_t *olen );
 
 /**
  * \brief          Translate hash algorithm OID into md_type
@@ -441,10 +442,11 @@
  *
  * \param md_alg   message digest algorithm
  * \param oid      place to store ASN.1 OID string pointer
+ * \param olen     length of the OID
  *
  * \return         0 if successful, or POLARSSL_ERR_OID_NOT_FOUND
  */
-int oid_get_oid_by_md( md_type_t md_alg, const char **oid_str );
+int oid_get_oid_by_md( md_type_t md_alg, const char **oid, size_t *olen );
 
 #if defined(POLARSSL_CIPHER_C)
 /**
diff --git a/library/oid.c b/library/oid.c
index c5608c3..f37bbf6 100644
--- a/library/oid.c
+++ b/library/oid.c
@@ -93,12 +93,13 @@
  * attribute from a oid_descriptor_t wrapper.
  */
 #define FN_OID_GET_OID_BY_ATTR1(FN_NAME, TYPE_T, LIST, ATTR1_TYPE, ATTR1)   \
-int FN_NAME( ATTR1_TYPE ATTR1, const char **oid_str )                       \
+int FN_NAME( ATTR1_TYPE ATTR1, const char **oid, size_t *olen )             \
 {                                                                           \
     const TYPE_T *cur = LIST;                                               \
     while( cur->descriptor.asn1 != NULL ) {                                 \
         if( cur->ATTR1 == ATTR1 ) {                                         \
-            *oid_str = cur->descriptor.asn1;                                \
+            *oid = cur->descriptor.asn1;                                    \
+            *olen = cur->descriptor.asn1_len;                               \
             return( 0 );                                                    \
         }                                                                   \
         cur++;                                                              \
@@ -112,12 +113,14 @@
  */
 #define FN_OID_GET_OID_BY_ATTR2(FN_NAME, TYPE_T, LIST, ATTR1_TYPE, ATTR1,   \
                                 ATTR2_TYPE, ATTR2)                          \
-int FN_NAME( ATTR1_TYPE ATTR1, ATTR2_TYPE ATTR2, const char **oid_str )     \
+int FN_NAME( ATTR1_TYPE ATTR1, ATTR2_TYPE ATTR2, const char **oid ,         \
+             size_t *olen )                                                 \
 {                                                                           \
     const TYPE_T *cur = LIST;                                               \
     while( cur->descriptor.asn1 != NULL ) {                                 \
         if( cur->ATTR1 == ATTR1 && cur->ATTR2 == ATTR2 ) {                  \
-            *oid_str = cur->descriptor.asn1;                                \
+            *oid = cur->descriptor.asn1;                                    \
+            *olen = cur->descriptor.asn1_len;                               \
             return( 0 );                                                    \
         }                                                                   \
         cur++;                                                              \
diff --git a/library/rsa.c b/library/rsa.c
index c39a338..10fd040 100644
--- a/library/rsa.c
+++ b/library/rsa.c
@@ -907,10 +907,9 @@
         if( md_info == NULL )
             return( POLARSSL_ERR_RSA_BAD_INPUT_DATA );
 
-        if( oid_get_oid_by_md( md_alg, &oid ) != 0 )
+        if( oid_get_oid_by_md( md_alg, &oid, &oid_size ) != 0 )
             return( POLARSSL_ERR_RSA_BAD_INPUT_DATA );
 
-        oid_size = strlen( oid );
         nb_pad -= 10 + oid_size;
 
         hashlen = md_get_size( md_info );
diff --git a/library/x509write.c b/library/x509write.c
index aed6624..f4f3c4d 100644
--- a/library/x509write.c
+++ b/library/x509write.c
@@ -581,7 +581,8 @@
 }
 
 static int x509_write_sig( unsigned char **p, unsigned char *start,
-                           const char *oid, unsigned char *sig, size_t size )
+                           const char *oid, size_t oid_len,
+                           unsigned char *sig, size_t size )
 {
     int ret;
     size_t len = 0;
@@ -602,7 +603,7 @@
     // Write OID
     //
     ASN1_CHK_ADD( len, asn1_write_algorithm_identifier( p, start, oid,
-                                                        strlen( oid ) ) );
+                                                        oid_len ) );
 
     return( len );
 }
@@ -693,6 +694,7 @@
 {
     int ret;
     const char *sig_oid;
+    size_t sig_oid_len = 0;
     unsigned char *c, *c2;
     unsigned char hash[64];
     unsigned char sig[POLARSSL_MPI_MAX_SIZE];
@@ -768,10 +770,12 @@
 
     // Generate correct OID
     //
-    ret = oid_get_oid_by_sig_alg( POLARSSL_PK_RSA, ctx->md_alg, &sig_oid );
+    ret = oid_get_oid_by_sig_alg( POLARSSL_PK_RSA, ctx->md_alg, &sig_oid,
+                                  &sig_oid_len );
 
     c2 = buf + size - 1;
-    ASN1_CHK_ADD( sig_len, x509_write_sig( &c2, buf, sig_oid, sig, ctx->rsa->len ) );
+    ASN1_CHK_ADD( sig_len, x509_write_sig( &c2, buf, sig_oid, sig_oid_len,
+                                           sig, ctx->rsa->len ) );
 
     c2 -= len;
     memcpy( c2, c, len );
@@ -787,6 +791,7 @@
 {
     int ret;
     const char *sig_oid;
+    size_t sig_oid_len = 0;
     unsigned char *c, *c2;
     unsigned char hash[64];
     unsigned char sig[POLARSSL_MPI_MAX_SIZE];
@@ -798,7 +803,8 @@
 
     // Generate correct OID
     //
-    ret = oid_get_oid_by_sig_alg( POLARSSL_PK_RSA, ctx->md_alg, &sig_oid );
+    ret = oid_get_oid_by_sig_alg( POLARSSL_PK_RSA, ctx->md_alg, &sig_oid,
+                                  &sig_oid_len );
     if( ret != 0 )
         return( ret );
 
@@ -893,7 +899,8 @@
     rsa_pkcs1_sign( ctx->issuer_key, NULL, NULL, RSA_PRIVATE, ctx->md_alg, 0, hash, sig );
 
     c2 = buf + size - 1;
-    ASN1_CHK_ADD( sig_len, x509_write_sig( &c2, buf, sig_oid, sig, ctx->issuer_key->len ) );
+    ASN1_CHK_ADD( sig_len, x509_write_sig( &c2, buf, sig_oid, sig_oid_len,
+                                           sig, ctx->issuer_key->len ) );
 
     c2 -= len;
     memcpy( c2, c, len );