diff --git a/include/polarssl/ecdsa.h b/include/polarssl/ecdsa.h
index 5eb83d9..47b644e 100644
--- a/include/polarssl/ecdsa.h
+++ b/include/polarssl/ecdsa.h
@@ -26,6 +26,23 @@
 
 #include "ecp.h"
 #include "md.h"
+/*
+ *  RFC 4492 page 20:
+ *
+ *      Ecdsa-Sig-Value ::= SEQUENCE {
+ *          r       INTEGER,
+ *          s       INTEGER
+ *      }
+ *
+ * Size is at most
+ *      1 (tag) + 1 (len) + 1 (initial 0) + ECP_MAX_BYTES for each of r and s,
+ *      twice that + 1 (tag) + 2 (len) for the sequence
+ * (assuming ECP_MAX_BYTES is less than 126 for r and s,
+ * and less than 124 (total len <= 255) for the sequence)
+ *
+ */
+/** Maximum size of an ECDSA signature in bytes */
+#define POLARSSL_ECDSA_MAX_LEN  ( 3 + 2 * ( 3 + POLARSSL_ECP_MAX_BYTES ) )
 
 /**
  * \brief           ECDSA context structure
@@ -58,6 +75,10 @@
  * \param f_rng     RNG function
  * \param p_rng     RNG parameter
  *
+ * \note            If the bitlength of the message hash is larger than the
+ *                  bitlength of the group order, then the hash is truncated as
+ *                  prescribed by SEC1 4.1.3 step 5.
+ *
  * \return          0 if successful,
  *                  or a POLARSSL_ERR_ECP_XXX or POLARSSL_MPI_XXX error code
  */
@@ -78,6 +99,10 @@
  * \param blen      Length of buf
  * \param md_alg    MD algorithm used to hash the message
  *
+ * \note            If the bitlength of the message hash is larger than the
+ *                  bitlength of the group order, then the hash is truncated as
+ *                  prescribed by SEC1 4.1.3 step 5.
+ *
  * \return          0 if successful,
  *                  or a POLARSSL_ERR_ECP_XXX or POLARSSL_MPI_XXX error code
  */
@@ -96,6 +121,10 @@
  * \param r         First integer of the signature
  * \param s         Second integer of the signature
  *
+ * \note            If the bitlength of the message hash is larger than the
+ *                  bitlength of the group order, then the hash is truncated as
+ *                  prescribed by SEC1 4.1.4 step 3.
+ *
  * \return          0 if successful,
  *                  POLARSSL_ERR_ECP_BAD_INPUT_DATA if signature is invalid
  *                  or a POLARSSL_ERR_ECP_XXX or POLARSSL_MPI_XXX error code
@@ -121,6 +150,10 @@
  *                  size of the curve used, plus 7 (eg. 71 bytes if a 256-bit
  *                  curve is used).
  *
+ * \note            If the bitlength of the message hash is larger than the
+ *                  bitlength of the group order, then the hash is truncated as
+ *                  prescribed by SEC1 4.1.3 step 5.
+ *
  * \return          0 if successful,
  *                  or a POLARSSL_ERR_ECP, POLARSSL_ERR_MPI or
  *                  POLARSSL_ERR_ASN1 error code
@@ -168,6 +201,10 @@
  * \param sig       Signature to read and verify
  * \param slen      Size of sig
  *
+ * \note            If the bitlength of the message hash is larger than the
+ *                  bitlength of the group order, then the hash is truncated as
+ *                  prescribed by SEC1 4.1.4 step 3.
+ *
  * \return          0 if successful,
  *                  POLARSSL_ERR_ECP_BAD_INPUT_DATA if signature is invalid,
  *                  POLARSSL_ERR_ECP_SIG_LEN_MISTMATCH if the signature is