diff --git a/modules/session/mod_session_crypto.c b/modules/session/mod_session_crypto.c

index 4d65bb8..9231a5e 100644

--- a/modules/session/mod_session_crypto.c

+++ b/modules/session/mod_session_crypto.c

@@ -18,6 +18,7 @@

 #include "apu_version.h"

 #include "apr_base64.h"                /* for apr_base64_decode et al */

 #include "apr_lib.h"

+#include "apr_md5.h"

 #include "apr_strings.h"

 #include "http_log.h"

 #include "http_core.h"

@@ -57,6 +58,146 @@ typedef struct {

     int library_set;

 } session_crypto_conf;

+/* Wrappers around apr_siphash24() and apr_crypto_equals(),

+ * available in APU-1.6/APR-2.0 only.

+ */

+#if APU_MAJOR_VERSION > 1 || (APU_MAJOR_VERSION == 1 && APU_MINOR_VERSION >= 6)

+

+#include "apr_siphash.h"

+

+#define AP_SIPHASH_DSIZE    APR_SIPHASH_DSIZE

+#define AP_SIPHASH_KSIZE    APR_SIPHASH_KSIZE

+#define ap_siphash24_auth   apr_siphash24_auth

+

+#define ap_crypto_equals    apr_crypto_equals

+

+#else

+

+#define AP_SIPHASH_DSIZE    8

+#define AP_SIPHASH_KSIZE    16

+

+#define ROTL64(x, n) (((x) << (n)) | ((x) >> (64 - (n))))

+

+#define U8TO64_LE(p) \

+    (((apr_uint64_t)((p)[0])      ) | \

+     ((apr_uint64_t)((p)[1]) <<  8) | \

+     ((apr_uint64_t)((p)[2]) << 16) | \

+     ((apr_uint64_t)((p)[3]) << 24) | \

+     ((apr_uint64_t)((p)[4]) << 32) | \

+     ((apr_uint64_t)((p)[5]) << 40) | \

+     ((apr_uint64_t)((p)[6]) << 48) | \

+     ((apr_uint64_t)((p)[7]) << 56))

+

+#define U64TO8_LE(p, v) \

+do { \

+    (p)[0] = (unsigned char)((v)      ); \

+    (p)[1] = (unsigned char)((v) >>  8); \

+    (p)[2] = (unsigned char)((v) >> 16); \

+    (p)[3] = (unsigned char)((v) >> 24); \

+    (p)[4] = (unsigned char)((v) >> 32); \

+    (p)[5] = (unsigned char)((v) >> 40); \

+    (p)[6] = (unsigned char)((v) >> 48); \

+    (p)[7] = (unsigned char)((v) >> 56); \

+} while (0)

+

+#define SIPROUND() \

+do { \

+    v0 += v1; v1=ROTL64(v1,13); v1 ^= v0; v0=ROTL64(v0,32); \

+    v2 += v3; v3=ROTL64(v3,16); v3 ^= v2; \

+    v0 += v3; v3=ROTL64(v3,21); v3 ^= v0; \

+    v2 += v1; v1=ROTL64(v1,17); v1 ^= v2; v2=ROTL64(v2,32); \

+} while(0)

+

+static apr_uint64_t ap_siphash24(const void *src, apr_size_t len,

+                                 const unsigned char key[AP_SIPHASH_KSIZE])

+{

+    const unsigned char *ptr, *end;

+    apr_uint64_t v0, v1, v2, v3, m;

+    apr_uint64_t k0, k1;

+    unsigned int rem;

+

+    k0 = U8TO64_LE(key + 0);

+    k1 = U8TO64_LE(key + 8);

+    v3 = k1 ^ (apr_uint64_t)0x7465646279746573ULL;

+    v2 = k0 ^ (apr_uint64_t)0x6c7967656e657261ULL;

+    v1 = k1 ^ (apr_uint64_t)0x646f72616e646f6dULL;

+    v0 = k0 ^ (apr_uint64_t)0x736f6d6570736575ULL;

+

+    rem = (unsigned int)(len & 0x7);

+    for (ptr = src, end = ptr + len - rem; ptr < end; ptr += 8) {

+        m = U8TO64_LE(ptr);

+        v3 ^= m;

+        SIPROUND();

+        SIPROUND();

+        v0 ^= m;

+    }

+    m = (apr_uint64_t)(len & 0xff) << 56;

+    switch (rem) {

+        case 7: m |= (apr_uint64_t)ptr[6] << 48;

+        case 6: m |= (apr_uint64_t)ptr[5] << 40;

+        case 5: m |= (apr_uint64_t)ptr[4] << 32;

+        case 4: m |= (apr_uint64_t)ptr[3] << 24;

+        case 3: m |= (apr_uint64_t)ptr[2] << 16;

+        case 2: m |= (apr_uint64_t)ptr[1] << 8;

+        case 1: m |= (apr_uint64_t)ptr[0];

+        case 0: break;

+    }

+    v3 ^= m;

+    SIPROUND();

+    SIPROUND();

+    v0 ^= m;

+

+    v2 ^= 0xff;

+    SIPROUND();

+    SIPROUND();

+    SIPROUND();

+    SIPROUND();

+

+    return v0 ^ v1 ^ v2 ^ v3;

+}

+

+static void ap_siphash24_auth(unsigned char out[AP_SIPHASH_DSIZE],

+                              const void *src, apr_size_t len,

+                              const unsigned char key[AP_SIPHASH_KSIZE])

+{

+    apr_uint64_t h;

+    h = ap_siphash24(src, len, key);

+    U64TO8_LE(out, h);

+}

+

+static int ap_crypto_equals(const void *buf1, const void *buf2,

+                            apr_size_t size)

+{

+    const unsigned char *p1 = buf1;

+    const unsigned char *p2 = buf2;

+    unsigned char diff = 0;

+    apr_size_t i;

+

+    for (i = 0; i < size; ++i) {

+        diff |= p1[i] ^ p2[i];

+    }

+

+    return 1 & ((diff - 1) >> 8);

+}

+

+#endif

+

+static void compute_auth(const void *src, apr_size_t len,

+                         const char *passphrase, apr_size_t passlen,

+                         unsigned char auth[AP_SIPHASH_DSIZE])

+{

+    unsigned char key[APR_MD5_DIGESTSIZE];

+

+    /* XXX: if we had a way to get the raw bytes from an apr_crypto_key_t

+     *      we could use them directly (not available in APR-1.5.x).

+     * MD5 is 128bit too, so use it to get a suitable siphash key

+     * from the passphrase.

+     */

+    apr_md5(key, passphrase, passlen);

+

+    ap_siphash24_auth(auth, src, len, key);

+}

+

 /**

  * Initialise the encryption as per the current config.

  *

@@ -128,21 +269,14 @@ static apr_status_t encrypt_string(request_rec * r, const apr_crypto_t *f,

     apr_crypto_block_t *block = NULL;

     unsigned char *encrypt = NULL;

     unsigned char *combined = NULL;

-    apr_size_t encryptlen, tlen;

+    apr_size_t encryptlen, tlen, combinedlen;

     char *base64;

     apr_size_t blockSize = 0;

     const unsigned char *iv = NULL;

     apr_uuid_t salt;

     apr_crypto_block_key_type_e *cipher;

     const char *passphrase;

-

-    /* by default, return an empty string */

-    *out = "";

-

-    /* don't attempt to encrypt an empty string, trying to do so causes a segfault */

-    if (!in || !*in) {

-        return APR_SUCCESS;

-    }

+    apr_size_t passlen;

     /* use a uuid as a salt value, and prepend it to our result */

     apr_uuid_get(&salt);

@@ -152,9 +286,9 @@ static apr_status_t encrypt_string(request_rec * r, const apr_crypto_t *f,

     }

     /* encrypt using the first passphrase in the list */

-    passphrase = APR_ARRAY_IDX(dconf->passphrases, 0, char *);

-    res = apr_crypto_passphrase(&key, &ivSize, passphrase,

-            strlen(passphrase),

+    passphrase = APR_ARRAY_IDX(dconf->passphrases, 0, const char *);

+    passlen = strlen(passphrase);

+    res = apr_crypto_passphrase(&key, &ivSize, passphrase, passlen,

             (unsigned char *) (&salt), sizeof(apr_uuid_t),

             *cipher, APR_MODE_CBC, 1, 4096, f, r->pool);

     if (APR_STATUS_IS_ENOKEY(res)) {

@@ -183,8 +317,9 @@ static apr_status_t encrypt_string(request_rec * r, const apr_crypto_t *f,

     }

     /* encrypt the given string */

-    res = apr_crypto_block_encrypt(&encrypt, &encryptlen, (unsigned char *)in,

-            strlen(in), block);

+    res = apr_crypto_block_encrypt(&encrypt, &encryptlen,

+                                   (const unsigned char *)in, strlen(in),

+                                   block);

     if (APR_SUCCESS != res) {

         ap_log_rerror(APLOG_MARK, APLOG_ERR, res, r, APLOGNO(01830)

                 "apr_crypto_block_encrypt failed");

@@ -198,18 +333,20 @@ static apr_status_t encrypt_string(request_rec * r, const apr_crypto_t *f,

     }

     encryptlen += tlen;

-    /* prepend the salt and the iv to the result */

-    combined = apr_palloc(r->pool, ivSize + encryptlen + sizeof(apr_uuid_t));

-    memcpy(combined, &salt, sizeof(apr_uuid_t));

-    memcpy(combined + sizeof(apr_uuid_t), iv, ivSize);

-    memcpy(combined + sizeof(apr_uuid_t) + ivSize, encrypt, encryptlen);

-

-    /* base64 encode the result */

-    base64 = apr_palloc(r->pool, apr_base64_encode_len(ivSize + encryptlen +

-                    sizeof(apr_uuid_t) + 1)

-            * sizeof(char));

-    apr_base64_encode(base64, (const char *) combined,

-            ivSize + encryptlen + sizeof(apr_uuid_t));

+    /* prepend the salt and the iv to the result (keep room for the MAC) */

+    combinedlen = AP_SIPHASH_DSIZE + sizeof(apr_uuid_t) + ivSize + encryptlen;

+    combined = apr_palloc(r->pool, combinedlen);

+    memcpy(combined + AP_SIPHASH_DSIZE, &salt, sizeof(apr_uuid_t));

+    memcpy(combined + AP_SIPHASH_DSIZE + sizeof(apr_uuid_t), iv, ivSize);

+    memcpy(combined + AP_SIPHASH_DSIZE + sizeof(apr_uuid_t) + ivSize,

+           encrypt, encryptlen);

+    /* authenticate the whole salt+IV+ciphertext with a leading MAC */

+    compute_auth(combined + AP_SIPHASH_DSIZE, combinedlen - AP_SIPHASH_DSIZE,

+                 passphrase, passlen, combined);

+

+    /* base64 encode the result (APR handles the trailing '\0') */

+    base64 = apr_palloc(r->pool, apr_base64_encode_len(combinedlen));

+    apr_base64_encode(base64, (const char *) combined, combinedlen);

     *out = base64;

     return res;

@@ -234,6 +371,7 @@ static apr_status_t decrypt_string(request_rec * r, const apr_crypto_t *f,

     char *decoded;

     apr_size_t blockSize = 0;

     apr_crypto_block_key_type_e *cipher;

+    unsigned char auth[AP_SIPHASH_DSIZE];

     int i = 0;

     /* strip base64 from the string */

@@ -241,6 +379,13 @@ static apr_status_t decrypt_string(request_rec * r, const apr_crypto_t *f,

     decodedlen = apr_base64_decode(decoded, in);

     decoded[decodedlen] = '\0';

+    /* sanity check - decoded too short? */

+    if (decodedlen < (AP_SIPHASH_DSIZE + sizeof(apr_uuid_t))) {

+        ap_log_rerror(APLOG_MARK, APLOG_DEBUG, APR_SUCCESS, r, APLOGNO()

+                "too short to decrypt, aborting");

+        return APR_ECRYPT;

+    }

+

     res = crypt_init(r, f, &cipher, dconf);

     if (res != APR_SUCCESS) {

         return res;

@@ -249,14 +394,25 @@ static apr_status_t decrypt_string(request_rec * r, const apr_crypto_t *f,

     /* try each passphrase in turn */

     for (; i < dconf->passphrases->nelts; i++) {

         const char *passphrase = APR_ARRAY_IDX(dconf->passphrases, i, char *);

-        apr_size_t len = decodedlen;

-        char *slider = decoded;

+        apr_size_t passlen = strlen(passphrase);

+        apr_size_t len = decodedlen - AP_SIPHASH_DSIZE;

+        unsigned char *slider = (unsigned char *)decoded + AP_SIPHASH_DSIZE;

+

+        /* Verify authentication of the whole salt+IV+ciphertext by computing

+         * the MAC and comparing it (timing safe) with the one in the payload.

+         */

+        compute_auth(slider, len, passphrase, passlen, auth);

+        if (!ap_crypto_equals(auth, decoded, AP_SIPHASH_DSIZE)) {

+            ap_log_rerror(APLOG_MARK, APLOG_DEBUG, res, r, APLOGNO()

+                    "auth does not match, skipping");

+            continue;

+        }

         /* encrypt using the first passphrase in the list */

-        res = apr_crypto_passphrase(&key, &ivSize, passphrase,

-                strlen(passphrase),

-                (unsigned char *)decoded, sizeof(apr_uuid_t),

-                *cipher, APR_MODE_CBC, 1, 4096, f, r->pool);

+        res = apr_crypto_passphrase(&key, &ivSize, passphrase, passlen,

+                                    slider, sizeof(apr_uuid_t),

+                                    *cipher, APR_MODE_CBC, 1, 4096,

+                                    f, r->pool);

         if (APR_STATUS_IS_ENOKEY(res)) {

             ap_log_rerror(APLOG_MARK, APLOG_DEBUG, res, r, APLOGNO(01832)

                     "the passphrase '%s' was empty", passphrase);

@@ -279,7 +435,7 @@ static apr_status_t decrypt_string(request_rec * r, const apr_crypto_t *f,

         }

         /* sanity check - decoded too short? */

-        if (decodedlen < (sizeof(apr_uuid_t) + ivSize)) {

+        if (len < (sizeof(apr_uuid_t) + ivSize)) {

             ap_log_rerror(APLOG_MARK, APLOG_DEBUG, APR_SUCCESS, r, APLOGNO(01836)

                     "too short to decrypt, skipping");

             res = APR_ECRYPT;

@@ -290,8 +446,8 @@ static apr_status_t decrypt_string(request_rec * r, const apr_crypto_t *f,

         slider += sizeof(apr_uuid_t);

         len -= sizeof(apr_uuid_t);

-        res = apr_crypto_block_decrypt_init(&block, &blockSize, (unsigned char *)slider, key,

-                r->pool);

+        res = apr_crypto_block_decrypt_init(&block, &blockSize, slider, key,

+                                            r->pool);

         if (APR_SUCCESS != res) {

             ap_log_rerror(APLOG_MARK, APLOG_DEBUG, res, r, APLOGNO(01837)

                     "apr_crypto_block_decrypt_init failed");

@@ -304,7 +460,7 @@ static apr_status_t decrypt_string(request_rec * r, const apr_crypto_t *f,

         /* decrypt the given string */

         res = apr_crypto_block_decrypt(&decrypted, &decryptedlen,

-                (unsigned char *)slider, len, block);

+                                       slider, len, block);

         if (res) {

             ap_log_rerror(APLOG_MARK, APLOG_DEBUG, res, r, APLOGNO(01838)

                     "apr_crypto_block_decrypt failed");