diff -ruN Crypt-OpenSSL-Bignum-0.09.orig/Bignum.pm Crypt-OpenSSL-Bignum-0.09/Bignum.pm
--- Crypt-OpenSSL-Bignum-0.09.orig/Bignum.pm	2017-12-01 20:07:57.000000000 +0100
+++ Crypt-OpenSSL-Bignum-0.09/Bignum.pm	2020-04-04 20:21:22.290086257 +0200
@@ -314,6 +314,15 @@
 a new Crypt::OpenSSL::Bignum object, using the second argument,
 a Crypt::OpenSSL::Bignum::CTX object, as a scratchpad.
 
+=item mod_sqrt
+
+ my $new_bn_object = $self->mod_sqrt($bn_n, $ctx);
+ # new object is created $self is not modified
+
+Computes the square root of C<$self> modulo C<$bn_n> and returns the result in
+a new Crypt::OpenSSL::Bignum object, using the second argument,
+a Crypt::OpenSSL::Bignum::CTX object, as a scratchpad.
+
 =item gcd
 
  my $new_bn_object = $self->gcd($bn_b, $ctx);
diff -ruN Crypt-OpenSSL-Bignum-0.09.orig/Bignum.xs Crypt-OpenSSL-Bignum-0.09/Bignum.xs
--- Crypt-OpenSSL-Bignum-0.09.orig/Bignum.xs	2017-12-01 20:05:15.000000000 +0100
+++ Crypt-OpenSSL-Bignum-0.09/Bignum.xs	2020-04-04 20:21:04.377184936 +0200
@@ -354,6 +354,20 @@
     RETVAL
 
 Crypt::OpenSSL::Bignum
+BN_mod_sqrt(self, n, ctx)
+    Crypt::OpenSSL::Bignum self;
+    Crypt::OpenSSL::Bignum n;
+    Crypt::OpenSSL::Bignum::CTX ctx;
+  PREINIT:
+    BIGNUM* bn;
+  CODE:
+    checkOpenSslCall( bn = BN_new() );
+    checkOpenSslCall( BN_mod_sqrt( bn, self, n, ctx ) );
+    RETVAL = bn;
+  OUTPUT:
+    RETVAL
+
+Crypt::OpenSSL::Bignum
 BN_gcd(self, b, ctx)
     Crypt::OpenSSL::Bignum self;
     Crypt::OpenSSL::Bignum b;
diff -ruN Crypt-OpenSSL-Bignum-0.09.orig/test.pl Crypt-OpenSSL-Bignum-0.09/test.pl
--- Crypt-OpenSSL-Bignum-0.09.orig/test.pl	2016-10-22 12:46:23.000000000 +0200
+++ Crypt-OpenSSL-Bignum-0.09/test.pl	2020-04-04 20:28:16.946804394 +0200
@@ -125,6 +125,9 @@
 ok( 36 == $bn6->sqr( $ctx )->get_word() );
 ok( 12 == $bn23->mod_inverse( $bn25, $ctx )->get_word() );
 
+my $bn18 = _new_bn( 18 );
+ok( 8 == $bn18->mod_sqrt( $bn23, $ctx )->get_word() );
+
 ok(Crypt::OpenSSL::Bignum->new()->get_word == 0);
 ok(Crypt::OpenSSL::Bignum->rand(32, 0, 0));
 ok(Crypt::OpenSSL::Bignum->pseudo_rand(32, 0, 0));