diff --git a/library/pkcs5.c b/library/pkcs5.c
index 8a80aa5..1533a92 100644
--- a/library/pkcs5.c
+++ b/library/pkcs5.c
@@ -79,6 +79,11 @@
 #define mbedtls_printf printf
 #endif
 
+/* Implementation that should never be optimized out by the compiler */
+static void mbedtls_zeroize( void *v, size_t n ) {
+    volatile unsigned char *p = (unsigned char*)v; while( n-- ) *p++ = 0;
+}
+
 #if defined(MBEDTLS_ASN1_PARSE_C)
 static int pkcs5_parse_pbkdf2_params( const mbedtls_asn1_buf *params,
                                       mbedtls_asn1_buf *salt, int *iterations,
@@ -312,6 +317,10 @@
                 break;
     }
 
+    /* Zeroise buffers to clear sensitive data from memory. */
+    mbedtls_zeroize( work, MBEDTLS_MD_MAX_SIZE );
+    mbedtls_zeroize( md1, MBEDTLS_MD_MAX_SIZE );
+
     return( 0 );
 }
 
diff --git a/library/sha1.c b/library/sha1.c
index 83ef9bd..65841ee 100644
--- a/library/sha1.c
+++ b/library/sha1.c
@@ -300,6 +300,15 @@
     ctx->state[3] += D;
     ctx->state[4] += E;
 
+    /* Zeroise buffers and variables to clear sensitive data from memory. */
+    mbedtls_zeroize( &A, sizeof( A ) );
+    mbedtls_zeroize( &B, sizeof( B ) );
+    mbedtls_zeroize( &C, sizeof( C ) );
+    mbedtls_zeroize( &D, sizeof( D ) );
+    mbedtls_zeroize( &E, sizeof( E ) );
+    mbedtls_zeroize( &W, sizeof( W ) );
+    mbedtls_zeroize( &temp, sizeof( temp ) );
+
     return( 0 );
 }
 
diff --git a/library/sha256.c b/library/sha256.c
index 6ae6a0e..9552b8c 100644
--- a/library/sha256.c
+++ b/library/sha256.c
@@ -269,6 +269,12 @@
     for( i = 0; i < 8; i++ )
         ctx->state[i] += A[i];
 
+    /* Zeroise buffers and variables to clear sensitive data from memory. */
+    mbedtls_zeroize( &A, sizeof( A ) );
+    mbedtls_zeroize( &W, sizeof( W ) );
+    mbedtls_zeroize( &temp1, sizeof( temp1 ) );
+    mbedtls_zeroize( &temp2, sizeof( temp2 ) );
+
     return( 0 );
 }
 
diff --git a/library/sha512.c b/library/sha512.c
index 0a42f55..9e9f073 100644
--- a/library/sha512.c
+++ b/library/sha512.c
@@ -300,6 +300,19 @@
     ctx->state[6] += G;
     ctx->state[7] += H;
 
+    /* Zeroise buffers and variables to clear sensitive data from memory. */
+    mbedtls_zeroize( &A, sizeof( A ) );
+    mbedtls_zeroize( &B, sizeof( B ) );
+    mbedtls_zeroize( &C, sizeof( C ) );
+    mbedtls_zeroize( &D, sizeof( D ) );
+    mbedtls_zeroize( &E, sizeof( E ) );
+    mbedtls_zeroize( &F, sizeof( F ) );
+    mbedtls_zeroize( &G, sizeof( G ) );
+    mbedtls_zeroize( &H, sizeof( H ) );
+    mbedtls_zeroize( &W, sizeof( W ) );
+    mbedtls_zeroize( &temp1, sizeof( temp1 ) );
+    mbedtls_zeroize( &temp2, sizeof( temp2 ) );
+
     return( 0 );
 }