diff --git a/src/doc/buffer-shldata.h/buffer_shldata_getinit.3.md b/src/doc/buffer-shldata.h/buffer_shldata_getinit.3.md
index a23e1dc..3657dbf 100644
--- a/src/doc/buffer-shldata.h/buffer_shldata_getinit.3.md
+++ b/src/doc/buffer-shldata.h/buffer_shldata_getinit.3.md
@@ -12,8 +12,8 @@ the shielded data protocol through buffer interface
     #include <limb/buffer-shldata.h>
 
 ```pre hl
-int buffer_shldata_getinit_sa(buffer *<em>buf</em>, const char *<em>pwd</em>, size_t <em>plen</em>, stralloc *<em>sa</em>, buffer_shldata_ctx *<em>ctx</em>)
-int buffer_shldata_getinit(buffer *<em>buf</em>, const char *<em>pwd</em>, size_t <em>plen</em>, buffer_shldata_ctx *<em>ctx</em>)
+int buffer_shldata_getinit_sa(buffer *<em>buf</em>, const char *<em>pwd</em>, size_t <em>plen</em>, unsigned *<em>algo</em>, unsigned *<em>iter</em>, stralloc *<em>sa</em>, buffer_shldata_ctx *<em>ctx</em>)
+int buffer_shldata_getinit(buffer *<em>buf</em>, const char *<em>pwd</em>, size_t <em>plen</em>, unsigned *<em>algo</em>, unsigned *<em>iter</em>, buffer_shldata_ctx *<em>ctx</em>)
 size_t buffer_shldata_datasize(buffer_shldata_ctx *<em>ctx</em>)
 ssize_t buffer_shldata_get(buffer *<em>buf</em>, char *<em>dst</em>, size_t <em>dlen</em>, buffer_shldata_ctx *<em>ctx</em>)
 int buffer_shldata_getfinal_sa(buffer *<em>buf</em>, stralloc *<em>sa</em>, buffer_shldata_ctx *<em>ctx</em>)
@@ -27,9 +27,10 @@ and decrypt it with a user-supplied password, as per the shielded data protocol
 described in [shldata](5).
 
 The `buffer_shldata_getinit`() function reads data from the buffer pointed by
-`buf` for derivation parameters, derives a secret key from the password pointed
-by `pwd` of length `plen` and initializes the opaque structure pointed by `ctx`
-for decryption.
+`buf` for derivation parameters, storing in the memory pointed to by `algo` and
+`iter` the used algorithm and iterations number, respectively.
+It then derives a secret key from the password pointed by `pwd` of length `plen`
+and initializes the opaque structure pointed by `ctx` for decryption.
 
 The `buffer_shldata_getinit_sa`() function is similar but using the *stralloc*
 `sa` as head-allocated temporary space.
diff --git a/src/doc/shldata-rw.h/shldata_write.3.md b/src/doc/shldata-rw.h/shldata_write.3.md
index b125016..173fab9 100644
--- a/src/doc/shldata-rw.h/shldata_write.3.md
+++ b/src/doc/shldata-rw.h/shldata_write.3.md
@@ -16,8 +16,8 @@ int shldata_chkmagic(u32 <em>magic</em>)
 int shldata_write(int <em>bfd</em>, const char *<em>file</em>, u32 <em>magic</em>, u64 <em>ver</em>,
                   const char *<em>pwd</em>, size_t <em>plen</em>, unsigned <em>algo</em>, unsigned <em>iter</em>,
                   int <em>inplace</em>, const struct iovec <em>v</em>[], unsigned <em>n</em>)
-int shldata_read(u32 *<em>magic</em>, u64 *<em>ver</em>, stralloc *<em>sa</em>, int <em>bfd</em>, const char *<em>file</em>,
-                 const char *<em>pwd</em>, size_t <em>plen</em>)
+int shldata_read(u32 *<em>magic</em>, u64 *<em>ver</em>, unsigned *<em>algo</em>, unsigned *<em>iter</em>, stralloc *<em>sa</em>,
+                 int <em>bfd</em>, const char *<em>file</em>, const char *<em>pwd</em>, size_t <em>plen</em>)
 ```
 
 # DESCRIPTION
@@ -52,9 +52,11 @@ to the directory associated with the file descriptor `bfd`.
 If passed the special value *AT_FDCWD* in the `bfd` parameter, the current
 working directory is used.
 
-If the magic is valid, parameters will read and the encrypted data will then be
-decrypted using the password pointed by `pwd` of length `plen` and placed into
-the *stralloc* pointed by `sa`.
+If the magic is valid, parameters will read; The algorithm and iterations number
+used for key derivation will be put as value pointed by `algo` and `iter`
+respectively, and used with the password pointed by `pwd` of length `plen` to
+derive the encryption key. The decrypted data will be placed into the *stralloc*
+pointed by `sa`.
 
 ! INFO:
 ! It is possible to set the value pointed to be `magic` to the expected magic
diff --git a/src/doc/shldata.h/shldata_initr.3.md b/src/doc/shldata.h/shldata_initr.3.md
index 600b85b..aa3bef6 100644
--- a/src/doc/shldata.h/shldata_initr.3.md
+++ b/src/doc/shldata.h/shldata_initr.3.md
@@ -11,7 +11,7 @@ data using the shielded data protocol
     #include <limb/shldata.h>
 
 ```pre hl
-ssize_t shldata_initr(const char *<em>sce</em>, size_t <em>slen</em>, const char *<em>pwd</em>, size_t <em>plen</em>, shldata_ctx *<em>ctx</em>)
+ssize_t shldata_initr(const char *<em>sce</em>, size_t <em>slen</em>, const char *<em>pwd</em>, size_t <em>plen</em>, unsigned *<em>algo</em>, unsigned *<em>iter</em>, shldata_ctx *<em>ctx</em>)
 size_t shldata_datasize(shldata_ctx *<em>ctx</em>)
 int shldata_decrypt(char *<em>dst</em>, const char *<em>sce</em>, size_t <em>len</em>, shldata_ctx *<em>ctx</em>)
 ssize_t shldata_finalr(const char *<em>sce</em>, size_t <em>slen</em>, shldata_ctx *<em>ctx</em>)
@@ -24,9 +24,11 @@ user-supplied password using the shielded data protocol, as described in
 [shldata](5).
 
 First, the `shldata_initr`() function will read the memory pointed by `sce` (up
-to a maximum of `slen` bytes) for derivation parameters, then it will derive a
-secret key from the password pointed by `pwd` of length `plen` and initialize
-the opaque structure pointed by `ctx`.
+to a maximum of `slen` bytes) for derivation parameters. The algorithm and
+number of iterations used will be stored in the variables pointed to by `algo`
+and `iter` respectively.
+Then it will derive a secret key from the password pointed by `pwd` of length
+`plen` and initialize the opaque structure pointed by `ctx`.
 
 The `shldata_datasize`() macro returns the length of the encrypted data, and
 therefore decrypted data.
diff --git a/src/include/buffer-shldata.h b/src/include/buffer-shldata.h
index 56c95b2..4275afe 100644
--- a/src/include/buffer-shldata.h
+++ b/src/include/buffer-shldata.h
@@ -6,9 +6,10 @@
 
 #include <skalibs/functypes.h>
 #include <limb/buffer-shldata.h>
+#include <limb/gccattributes.h>
 
 typedef ssize_t (*shldata_getfull) (const char *s, size_t l, void *args, buffer_shldata_ctx *ctx);
 
-extern int buffer_shldata_getfull(buffer *b, shldata_getfull fn, void *args, stralloc *sa, buffer_shldata_ctx *ctx);
+extern int buffer_shldata_getfull(buffer *b, shldata_getfull fn, void *args, stralloc *sa, buffer_shldata_ctx *ctx) gccattr_hidden;
 
 #endif /* LIMB_LIMB_BUFFER_SHLDATA_h */
diff --git a/src/liblimb/buffer-shldata.h/buffer_shldata_getinit.c b/src/liblimb/buffer-shldata.h/buffer_shldata_getinit.c
index e8a5f75..1d4379b 100644
--- a/src/liblimb/buffer-shldata.h/buffer_shldata_getinit.c
+++ b/src/liblimb/buffer-shldata.h/buffer_shldata_getinit.c
@@ -4,7 +4,7 @@
 #include <limb/buffer-shldata.h>
 
 int
-buffer_shldata_getinit(buffer *b, const char *pwd, size_t plen, buffer_shldata_ctx *ctx)
+buffer_shldata_getinit(buffer *b, const char *pwd, size_t plen, unsigned *algo, unsigned *iter, buffer_shldata_ctx *ctx)
 {
-    return buffer_shldata_getinit_sa(b, pwd, plen, &ctx->sa, ctx);
+    return buffer_shldata_getinit_sa(b, pwd, plen, algo, iter, &ctx->sa, ctx);
 }
diff --git a/src/liblimb/buffer-shldata.h/buffer_shldata_getinit_sa.c b/src/liblimb/buffer-shldata.h/buffer_shldata_getinit_sa.c
index c656529..8a2034a 100644
--- a/src/liblimb/buffer-shldata.h/buffer_shldata_getinit_sa.c
+++ b/src/liblimb/buffer-shldata.h/buffer_shldata_getinit_sa.c
@@ -5,6 +5,8 @@
 #include "buffer-shldata.h"
 
 struct args {
+    unsigned *algo;
+    unsigned *iter;
     const char *pwd;
     size_t plen;
 };
@@ -13,13 +15,14 @@ static ssize_t
 fn(const char *s, size_t l, void *args_, buffer_shldata_ctx *ctx)
 {
     struct args *args = args_;
-    return shldata_initr(s, l, args->pwd, args->plen, &ctx->sd);
+    return shldata_initr(s, l, args->pwd, args->plen, args->algo, args->iter, &ctx->sd);
 }
 
 int
 buffer_shldata_getinit_sa(buffer *b, const char *pwd, size_t plen,
-                          stralloc *sa, buffer_shldata_ctx *ctx)
+                          unsigned *algo, unsigned *iter, stralloc *sa,
+                          buffer_shldata_ctx *ctx)
 {
-    struct args args = { pwd, plen };
+    struct args args = { algo, iter, pwd, plen };
     return buffer_shldata_getfull(b, fn, &args, sa, ctx);
 }
diff --git a/src/liblimb/include/limb/buffer-shldata.h b/src/liblimb/include/limb/buffer-shldata.h
index 1c43d72..2ea04dd 100644
--- a/src/liblimb/include/limb/buffer-shldata.h
+++ b/src/liblimb/include/limb/buffer-shldata.h
@@ -28,8 +28,8 @@ extern ssize_t buffer_shldata_putfinal(buffer *b, buffer_shldata_ctx *ctx);
 
 /* Reading */
 
-extern int buffer_shldata_getinit_sa(buffer *b, const char *pwd, size_t plen, stralloc *sa, buffer_shldata_ctx *ctx);
-extern int buffer_shldata_getinit(buffer *b, const char *pwd, size_t plen, buffer_shldata_ctx *ctx);
+extern int buffer_shldata_getinit_sa(buffer *b, const char *pwd, size_t plen, unsigned *algo, unsigned *iter, stralloc *sa, buffer_shldata_ctx *ctx);
+extern int buffer_shldata_getinit(buffer *b, const char *pwd, size_t plen, unsigned *algo, unsigned *iter, buffer_shldata_ctx *ctx);
 #define buffer_shldata_datasize(ctx)     shldata_datasize(&(ctx)->sd)
 extern ssize_t buffer_shldata_get(buffer *b, char *dst, size_t dlen, buffer_shldata_ctx *ctx);
 extern int buffer_shldata_getfinal_sa(buffer *b, stralloc *sa, buffer_shldata_ctx *ctx);
diff --git a/src/liblimb/include/limb/shldata-rw.h b/src/liblimb/include/limb/shldata-rw.h
index 05321bb..4757ecf 100644
--- a/src/liblimb/include/limb/shldata-rw.h
+++ b/src/liblimb/include/limb/shldata-rw.h
@@ -16,7 +16,7 @@ extern int shldata_chkmagic(u32 magic);
 extern int shldata_write(int bfd, const char *file, u32 magic, u64 ver,
                          const char *pwd, size_t plen, unsigned algo, unsigned iter,
                          int inplace, const struct iovec v[], unsigned n);
-extern int shldata_read(u32 *magic, u64 *ver, stralloc *sa, int bfd, const char *file,
-                        const char *pwd, size_t plen);
+extern int shldata_read(u32 *magic, u64 *ver, unsigned *algo, unsigned *iter, stralloc *sa,
+                        int bfd, const char *file, const char *pwd, size_t plen);
 
 #endif /* LIMB_SHLDATA_RW_H */
diff --git a/src/liblimb/include/limb/shldata.h b/src/liblimb/include/limb/shldata.h
index 9081fce..2df726f 100644
--- a/src/liblimb/include/limb/shldata.h
+++ b/src/liblimb/include/limb/shldata.h
@@ -22,7 +22,7 @@ extern ssize_t shldata_predata(char *dst, size_t dlen, shldata_ctx *ctx);
 extern ssize_t shldata_finalw(char *dst, size_t dlen, shldata_ctx *ctx);
 
 
-extern ssize_t shldata_initr(const char *sce, size_t slen, const char *pwd, size_t plen, shldata_ctx *ctx);
+extern ssize_t shldata_initr(const char *sce, size_t slen, const char *pwd, size_t plen, unsigned *algo, unsigned *iter, shldata_ctx *ctx);
 #define shldata_datasize(ctx)       (ctx)->len
 extern int shldata_decrypt(char *dst, const char *sce, size_t len, shldata_ctx *ctx);
 extern ssize_t shldata_finalr(const char *sce, size_t slen, shldata_ctx *ctx);
diff --git a/src/liblimb/shldata-rw.h/shldata_read.c b/src/liblimb/shldata-rw.h/shldata_read.c
index 615206e..9a30b45 100644
--- a/src/liblimb/shldata-rw.h/shldata_read.c
+++ b/src/liblimb/shldata-rw.h/shldata_read.c
@@ -17,8 +17,8 @@ chkmagic(u32 magic, u32 wmagic)
 }
 
 int
-shldata_read(u32 *magic, u64 *ver, stralloc *sa, int bfd, const char *file,
-             const char *pwd, size_t plen)
+shldata_read(u32 *magic, u64 *ver, unsigned *algo, unsigned *iter, stralloc *sa,
+             int bfd, const char *file, const char *pwd, size_t plen)
 {
     int ret = 0;
     char buf[4096];
@@ -35,7 +35,7 @@ shldata_read(u32 *magic, u64 *ver, stralloc *sa, int bfd, const char *file,
     size_t salen = sa->len;
     if (!buffer_gethdr(&b, magic, ver)
             || !chkmagic(*magic, wmagic)
-            || !buffer_shldata_getinit_sa(&b, pwd, plen, sa, &bsd)
+            || !buffer_shldata_getinit_sa(&b, pwd, plen, algo, iter, sa, &bsd)
             || !stralloc_readyplus(sa, buffer_shldata_datasize(&bsd))
             || !buffer_shldata_get(&b, sa->s + sa->len, buffer_shldata_datasize(&bsd), &bsd)
             || (sa->len += buffer_shldata_datasize(&bsd), 0)
diff --git a/src/liblimb/shldata.h/shldata_initr.c b/src/liblimb/shldata.h/shldata_initr.c
index 1e3e922..1dee37d 100644
--- a/src/liblimb/shldata.h/shldata_initr.c
+++ b/src/liblimb/shldata.h/shldata_initr.c
@@ -9,9 +9,10 @@
 #include "shldata.h"
 
 ssize_t
-shldata_initr(const char *sce, size_t slen, const char *pwd, size_t plen, shldata_ctx *ctx)
+shldata_initr(const char *sce, size_t slen, const char *pwd, size_t plen,
+              unsigned *algo, unsigned *iter, shldata_ctx *ctx)
 {
-    unsigned algo, iter, o;
+    unsigned o;
     const char *salt;
     size_t sltlen;
     ssize_t aadoff;
@@ -22,7 +23,7 @@ shldata_initr(const char *sce, size_t slen, const char *pwd, size_t plen, shldat
     sltlen = 0;
 
     aadoff = -1;
-    o = algo = iter = 0;
+    o = *algo = *iter = 0;
     for (;;) {
         u64 id, u;
 
@@ -39,10 +40,10 @@ shldata_initr(const char *sce, size_t slen, const char *pwd, size_t plen, shldat
             aadoff = o;
         switch (id) {
             case ID_ALGO:
-                algo = u + 1;
+                *algo = u + 1;
                 break;
             case ID_ITER:
-                iter = u;
+                *iter = u;
                 break;
             case ID_SALT:
                 salt = sce + o + r;
@@ -60,13 +61,13 @@ shldata_initr(const char *sce, size_t slen, const char *pwd, size_t plen, shldat
             break;
         o += r;
     }
-    if (!algo || !iter || !sltlen)
+    if (!*algo || !*iter || !sltlen)
         return (errno = EINVAL, -1);
-    --algo;
+    --*algo;
 
     char key[KEY_LEN];
     char nonce[NONCE_LEN] = { 0 };
-    pbkdf2(key, sizeof(key), hashers[algo], pwd, plen, salt, sltlen, iter);
+    pbkdf2(key, sizeof(key), hashers[*algo], pwd, plen, salt, sltlen, *iter);
     ccpl_init(key, nonce, &ctx->ccpl);
     ccpl_aad(sce + aadoff, o - aadoff, &ctx->ccpl);