diff --git a/.travis.yml b/.travis.yml
index 9c4120a8..24fa6c73 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -3,8 +3,11 @@ rust:
   - stable
 #  - 1.31.0
 #  - 1.22.0
+before_script:
+  - rustup component add rustfmt
 script:
   - cd $TRAVIS_BUILD_DIR/core/lib/
+  - cargo fmt -- --check --verbose
   - cargo build --verbose --all
   - cargo test --verbose --all
 
diff --git a/core/lib/Cargo.toml b/core/lib/Cargo.toml
index df5a5abd..d9b119a0 100644
--- a/core/lib/Cargo.toml
+++ b/core/lib/Cargo.toml
@@ -2,7 +2,10 @@
 name = "magical-bitcoin-wallet"
 version = "0.1.0"
 authors = ["Riccardo Casatta <riccardo@casatta.it>", "Alekos Filini <alekos.filini@gmail.com>"]
-edition = "2018"
 
 [dependencies]
-"electrum-client" = { version = "0.1.0-beta.1", optional = true }
+log = "^0.4"
+bitcoin = { version = "0.23", features = ["use-serde"] }
+miniscript = { version = "0.12" }
+serde = { version = "^1.0", features = ["derive"] }
+serde_json = { version = "^1.0" }
diff --git a/core/lib/examples/parse_descriptor.rs b/core/lib/examples/parse_descriptor.rs
new file mode 100644
index 00000000..2af42b3a
--- /dev/null
+++ b/core/lib/examples/parse_descriptor.rs
@@ -0,0 +1,27 @@
+extern crate magical_bitcoin_wallet;
+
+use std::str::FromStr;
+
+use magical_bitcoin_wallet::bitcoin::*;
+use magical_bitcoin_wallet::descriptor::*;
+
+fn main() {
+    let desc = "sh(wsh(or_d(\
+                    thresh_m(\
+                      2,[d34db33f/44'/0'/0']xpub6ERApfZwUNrhLCkDtcHTcxd75RbzS1ed54G1LkBUHQVHQKqhMkhgbmJbZRkrgZw4koxb5JaHWkY4ALHY2grBGRjaDMzQLcgJvLJuZZvRcEL/1/*,tprv8ZgxMBicQKsPduL5QnGihpprdHyypMGi4DhimjtzYemu7se5YQNcZfAPLqXRuGHb5ZX2eTQj62oNqMnyxJ7B7wz54Uzswqw8fFqMVdcmVF7/1/*\
+                    ),\
+                    and_v(vc:pk_h(cVt4o7BGAig1UXywgGSmARhxMdzP5qvQsxKkSsc1XEkw3tDTQFpy),older(1000))\
+                   )))";
+
+    let extended_desc = ExtendedDescriptor::from_str(desc).unwrap();
+    println!("{:?}", extended_desc);
+
+    let derived_desc = extended_desc.derive(42).unwrap();
+    println!("{:?}", derived_desc);
+
+    let addr = derived_desc.address(Network::Testnet).unwrap();
+    println!("{}", addr);
+
+    let script = derived_desc.witness_script();
+    println!("{:?}", script);
+}
diff --git a/core/lib/src/descriptor/error.rs b/core/lib/src/descriptor/error.rs
new file mode 100644
index 00000000..f9a10870
--- /dev/null
+++ b/core/lib/src/descriptor/error.rs
@@ -0,0 +1,26 @@
+#[derive(Debug)]
+pub enum Error {
+    InternalError,
+    InvalidPrefix(Vec<u8>),
+    HardenedDerivationOnXpub,
+    MalformedInput,
+    KeyParsingError(String),
+
+    BIP32(bitcoin::util::bip32::Error),
+    Base58(bitcoin::util::base58::Error),
+    PK(bitcoin::util::key::Error),
+    Miniscript(miniscript::Error),
+    Hex(bitcoin::hashes::hex::Error),
+}
+
+impl std::fmt::Display for Error {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{:?}", self)
+    }
+}
+
+impl_error!(bitcoin::util::bip32::Error, BIP32);
+impl_error!(bitcoin::util::base58::Error, Base58);
+impl_error!(bitcoin::util::key::Error, PK);
+impl_error!(miniscript::Error, Miniscript);
+impl_error!(bitcoin::hashes::hex::Error, Hex);
diff --git a/core/lib/src/descriptor/extended_key.rs b/core/lib/src/descriptor/extended_key.rs
new file mode 100644
index 00000000..0f7bd9e9
--- /dev/null
+++ b/core/lib/src/descriptor/extended_key.rs
@@ -0,0 +1,349 @@
+use std::fmt::{self, Display};
+use std::str::FromStr;
+
+use bitcoin::hashes::hex::{FromHex, ToHex};
+use bitcoin::secp256k1;
+use bitcoin::util::base58;
+use bitcoin::util::bip32::{
+    ChildNumber, DerivationPath, ExtendedPrivKey, ExtendedPubKey, Fingerprint,
+};
+use bitcoin::PublicKey;
+
+#[allow(unused_imports)]
+use log::{debug, error, info, trace};
+
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub enum DerivationIndex {
+    Fixed,
+    Normal,
+    Hardened,
+}
+
+impl DerivationIndex {
+    fn as_path(&self, index: u32) -> DerivationPath {
+        match self {
+            DerivationIndex::Fixed => vec![],
+            DerivationIndex::Normal => vec![ChildNumber::Normal { index }],
+            DerivationIndex::Hardened => vec![ChildNumber::Hardened { index }],
+        }
+        .into()
+    }
+}
+
+impl Display for DerivationIndex {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let chars = match *self {
+            Self::Fixed => "",
+            Self::Normal => "/*",
+            Self::Hardened => "/*'",
+        };
+
+        write!(f, "{}", chars)
+    }
+}
+
+#[derive(Clone, Debug)]
+pub struct DescriptorExtendedKey {
+    pub master_fingerprint: Option<Fingerprint>,
+    pub master_derivation: Option<DerivationPath>,
+    pub pubkey: ExtendedPubKey,
+    pub secret: Option<ExtendedPrivKey>,
+    pub path: DerivationPath,
+    pub final_index: DerivationIndex,
+}
+
+impl DescriptorExtendedKey {
+    pub fn full_path(&self, index: u32) -> DerivationPath {
+        let mut final_path: Vec<ChildNumber> = self.path.clone().into();
+        let other_path: Vec<ChildNumber> = self.final_index.as_path(index).into();
+        final_path.extend_from_slice(&other_path);
+
+        final_path.into()
+    }
+
+    pub fn derive<C: secp256k1::Verification + secp256k1::Signing>(
+        &self,
+        ctx: &secp256k1::Secp256k1<C>,
+        index: u32,
+    ) -> Result<PublicKey, super::Error> {
+        Ok(self.derive_xpub(ctx, index)?.public_key)
+    }
+
+    pub fn derive_xpub<C: secp256k1::Verification + secp256k1::Signing>(
+        &self,
+        ctx: &secp256k1::Secp256k1<C>,
+        index: u32,
+    ) -> Result<ExtendedPubKey, super::Error> {
+        if let Some(xprv) = self.secret {
+            let derive_priv = xprv.derive_priv(ctx, &self.full_path(index))?;
+            Ok(ExtendedPubKey::from_private(ctx, &derive_priv))
+        } else {
+            Ok(self.pubkey.derive_pub(ctx, &self.full_path(index))?)
+        }
+    }
+
+    pub fn root_xpub<C: secp256k1::Verification + secp256k1::Signing>(
+        &self,
+        ctx: &secp256k1::Secp256k1<C>,
+    ) -> ExtendedPubKey {
+        if let Some(ref xprv) = self.secret {
+            ExtendedPubKey::from_private(ctx, xprv)
+        } else {
+            self.pubkey
+        }
+    }
+}
+
+impl Display for DescriptorExtendedKey {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if let Some(ref fingerprint) = self.master_fingerprint {
+            write!(f, "[{}", fingerprint.to_hex())?;
+            if let Some(ref path) = self.master_derivation {
+                write!(f, "{}", &path.to_string()[1..])?;
+            }
+            write!(f, "]")?;
+        }
+
+        if let Some(xprv) = self.secret {
+            write!(f, "{}", xprv)?
+        } else {
+            write!(f, "{}", self.pubkey)?
+        }
+
+        write!(f, "{}{}", &self.path.to_string()[1..], self.final_index)
+    }
+}
+
+impl FromStr for DescriptorExtendedKey {
+    type Err = super::Error;
+
+    fn from_str(inp: &str) -> Result<DescriptorExtendedKey, Self::Err> {
+        let len = inp.len();
+
+        let (master_fingerprint, master_derivation, offset) = match inp.starts_with("[") {
+            false => (None, None, 0),
+            true => {
+                if inp.len() < 9 {
+                    return Err(super::Error::MalformedInput);
+                }
+
+                let master_fingerprint = &inp[1..9];
+                let close_bracket_index =
+                    &inp[9..].find("]").ok_or(super::Error::MalformedInput)?;
+                let path = if *close_bracket_index > 0 {
+                    Some(DerivationPath::from_str(&format!(
+                        "m{}",
+                        &inp[9..9 + *close_bracket_index]
+                    ))?)
+                } else {
+                    None
+                };
+
+                (
+                    Some(Fingerprint::from_hex(master_fingerprint)?),
+                    path,
+                    9 + *close_bracket_index + 1,
+                )
+            }
+        };
+
+        let (key_range, offset) = match &inp[offset..].find("/") {
+            Some(index) => (offset..offset + *index, offset + *index),
+            None => (offset..len, len),
+        };
+        let data = base58::from_check(&inp[key_range.clone()])?;
+        let secp = secp256k1::Secp256k1::new();
+        let (pubkey, secret) = match &data[0..4] {
+            [0x04u8, 0x88, 0xB2, 0x1E] | [0x04u8, 0x35, 0x87, 0xCF] => {
+                (ExtendedPubKey::from_str(&inp[key_range])?, None)
+            }
+            [0x04u8, 0x88, 0xAD, 0xE4] | [0x04u8, 0x35, 0x83, 0x94] => {
+                let private = ExtendedPrivKey::from_str(&inp[key_range])?;
+                (ExtendedPubKey::from_private(&secp, &private), Some(private))
+            }
+            data => return Err(super::Error::InvalidPrefix(data.into())),
+        };
+
+        let (path, final_index, _) = match &inp[offset..].starts_with("/") {
+            false => (DerivationPath::from(vec![]), DerivationIndex::Fixed, offset),
+            true => {
+                let (all, skip) = match &inp[len - 2..len] {
+                    "/*" => (DerivationIndex::Normal, 2),
+                    "*'" | "*h" => (DerivationIndex::Hardened, 3),
+                    _ => (DerivationIndex::Fixed, 0),
+                };
+
+                if all == DerivationIndex::Hardened && secret.is_none() {
+                    return Err(super::Error::HardenedDerivationOnXpub);
+                }
+
+                (
+                    DerivationPath::from_str(&format!("m{}", &inp[offset..len - skip]))?,
+                    all,
+                    len,
+                )
+            }
+        };
+
+        Ok(DescriptorExtendedKey {
+            master_fingerprint,
+            master_derivation,
+            pubkey,
+            secret,
+            path,
+            final_index,
+        })
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use std::str::FromStr;
+
+    use bitcoin::hashes::hex::FromHex;
+    use bitcoin::util::bip32::{ChildNumber, DerivationPath};
+
+    use crate::descriptor::*;
+
+    macro_rules! hex_fingerprint {
+        ($hex:expr) => {
+            Fingerprint::from_hex($hex).unwrap()
+        };
+    }
+
+    macro_rules! deriv_path {
+        ($str:expr) => {
+            DerivationPath::from_str($str).unwrap()
+        };
+
+        () => {
+            DerivationPath::from(vec![])
+        };
+    }
+
+    #[test]
+    fn test_derivation_index_fixed() {
+        let index = DerivationIndex::Fixed;
+        assert_eq!(index.as_path(1337), DerivationPath::from(vec![]));
+        assert_eq!(format!("{}", index), "");
+    }
+
+    #[test]
+    fn test_derivation_index_normal() {
+        let index = DerivationIndex::Normal;
+        assert_eq!(
+            index.as_path(1337),
+            DerivationPath::from(vec![ChildNumber::Normal { index: 1337 }])
+        );
+        assert_eq!(format!("{}", index), "/*");
+    }
+
+    #[test]
+    fn test_derivation_index_hardened() {
+        let index = DerivationIndex::Hardened;
+        assert_eq!(
+            index.as_path(1337),
+            DerivationPath::from(vec![ChildNumber::Hardened { index: 1337 }])
+        );
+        assert_eq!(format!("{}", index), "/*'");
+    }
+
+    #[test]
+    fn test_parse_xpub_no_path_fixed() {
+        let key = "xpub6ERApfZwUNrhLCkDtcHTcxd75RbzS1ed54G1LkBUHQVHQKqhMkhgbmJbZRkrgZw4koxb5JaHWkY4ALHY2grBGRjaDMzQLcgJvLJuZZvRcEL";
+        let ek = DescriptorExtendedKey::from_str(key).unwrap();
+        assert_eq!(ek.pubkey.fingerprint(), hex_fingerprint!("31a507b8"));
+        assert_eq!(ek.path, deriv_path!());
+        assert_eq!(ek.final_index, DerivationIndex::Fixed);
+    }
+
+    #[test]
+    fn test_parse_xpub_with_path_fixed() {
+        let key = "xpub6ERApfZwUNrhLCkDtcHTcxd75RbzS1ed54G1LkBUHQVHQKqhMkhgbmJbZRkrgZw4koxb5JaHWkY4ALHY2grBGRjaDMzQLcgJvLJuZZvRcEL/1/2/3";
+        let ek = DescriptorExtendedKey::from_str(key).unwrap();
+        assert_eq!(ek.pubkey.fingerprint(), hex_fingerprint!("31a507b8"));
+        assert_eq!(ek.path, deriv_path!("m/1/2/3"));
+        assert_eq!(ek.final_index, DerivationIndex::Fixed);
+    }
+
+    #[test]
+    fn test_parse_xpub_with_path_normal() {
+        let key = "xpub6ERApfZwUNrhLCkDtcHTcxd75RbzS1ed54G1LkBUHQVHQKqhMkhgbmJbZRkrgZw4koxb5JaHWkY4ALHY2grBGRjaDMzQLcgJvLJuZZvRcEL/1/2/3/*";
+        let ek = DescriptorExtendedKey::from_str(key).unwrap();
+        assert_eq!(ek.pubkey.fingerprint(), hex_fingerprint!("31a507b8"));
+        assert_eq!(ek.path, deriv_path!("m/1/2/3"));
+        assert_eq!(ek.final_index, DerivationIndex::Normal);
+    }
+
+    #[test]
+    #[should_panic(expected = "HardenedDerivationOnXpub")]
+    fn test_parse_xpub_with_path_hardened() {
+        let key = "xpub6ERApfZwUNrhLCkDtcHTcxd75RbzS1ed54G1LkBUHQVHQKqhMkhgbmJbZRkrgZw4koxb5JaHWkY4ALHY2grBGRjaDMzQLcgJvLJuZZvRcEL/*'";
+        let ek = DescriptorExtendedKey::from_str(key).unwrap();
+        assert_eq!(ek.pubkey.fingerprint(), hex_fingerprint!("31a507b8"));
+        assert_eq!(ek.path, deriv_path!("m/1/2/3"));
+        assert_eq!(ek.final_index, DerivationIndex::Fixed);
+    }
+
+    #[test]
+    fn test_parse_tprv_with_path_hardened() {
+        let key = "tprv8ZgxMBicQKsPduL5QnGihpprdHyypMGi4DhimjtzYemu7se5YQNcZfAPLqXRuGHb5ZX2eTQj62oNqMnyxJ7B7wz54Uzswqw8fFqMVdcmVF7/1/2/3/*'";
+        let ek = DescriptorExtendedKey::from_str(key).unwrap();
+        assert!(ek.secret.is_some());
+        assert_eq!(ek.pubkey.fingerprint(), hex_fingerprint!("5ea4190e"));
+        assert_eq!(ek.path, deriv_path!("m/1/2/3"));
+        assert_eq!(ek.final_index, DerivationIndex::Hardened);
+    }
+
+    #[test]
+    fn test_parse_xpub_master_details() {
+        let key = "[d34db33f/44'/0'/0']xpub6ERApfZwUNrhLCkDtcHTcxd75RbzS1ed54G1LkBUHQVHQKqhMkhgbmJbZRkrgZw4koxb5JaHWkY4ALHY2grBGRjaDMzQLcgJvLJuZZvRcEL";
+        let ek = DescriptorExtendedKey::from_str(key).unwrap();
+        assert_eq!(ek.master_fingerprint, Some(hex_fingerprint!("d34db33f")));
+        assert_eq!(ek.master_derivation, Some(deriv_path!("m/44'/0'/0'")));
+    }
+
+    #[test]
+    fn test_parse_xpub_master_details_empty_derivation() {
+        let key = "[d34db33f]xpub6ERApfZwUNrhLCkDtcHTcxd75RbzS1ed54G1LkBUHQVHQKqhMkhgbmJbZRkrgZw4koxb5JaHWkY4ALHY2grBGRjaDMzQLcgJvLJuZZvRcEL";
+        let ek = DescriptorExtendedKey::from_str(key).unwrap();
+        assert_eq!(ek.master_fingerprint, Some(hex_fingerprint!("d34db33f")));
+        assert_eq!(ek.master_derivation, None);
+    }
+
+    #[test]
+    #[should_panic(expected = "MalformedInput")]
+    fn test_parse_xpub_short_input() {
+        let key = "[d34d";
+        DescriptorExtendedKey::from_str(key).unwrap();
+    }
+
+    #[test]
+    #[should_panic(expected = "MalformedInput")]
+    fn test_parse_xpub_missing_closing_bracket() {
+        let key = "[d34db33fxpub6ERApfZwUNrhLCkDtcHTcxd75RbzS1ed54G1LkBUHQVHQKqhMkhgbmJbZRkrgZw4koxb5JaHWkY4ALHY2grBGRjaDMzQLcgJvLJuZZvRcEL";
+        DescriptorExtendedKey::from_str(key).unwrap();
+    }
+
+    #[test]
+    #[should_panic(expected = "InvalidChar")]
+    fn test_parse_xpub_invalid_fingerprint() {
+        let key = "[d34db33z]xpub6ERApfZwUNrhLCkDtcHTcxd75RbzS1ed54G1LkBUHQVHQKqhMkhgbmJbZRkrgZw4koxb5JaHWkY4ALHY2grBGRjaDMzQLcgJvLJuZZvRcEL";
+        DescriptorExtendedKey::from_str(key).unwrap();
+    }
+
+    #[test]
+    fn test_xpub_normal_full_path() {
+        let key = "xpub6ERApfZwUNrhLCkDtcHTcxd75RbzS1ed54G1LkBUHQVHQKqhMkhgbmJbZRkrgZw4koxb5JaHWkY4ALHY2grBGRjaDMzQLcgJvLJuZZvRcEL/1/2/*";
+        let ek = DescriptorExtendedKey::from_str(key).unwrap();
+        assert_eq!(ek.full_path(42), deriv_path!("m/1/2/42"));
+    }
+
+    #[test]
+    fn test_xpub_fixed_full_path() {
+        let key = "xpub6ERApfZwUNrhLCkDtcHTcxd75RbzS1ed54G1LkBUHQVHQKqhMkhgbmJbZRkrgZw4koxb5JaHWkY4ALHY2grBGRjaDMzQLcgJvLJuZZvRcEL/1/2";
+        let ek = DescriptorExtendedKey::from_str(key).unwrap();
+        assert_eq!(ek.full_path(42), deriv_path!("m/1/2"));
+        assert_eq!(ek.full_path(1337), deriv_path!("m/1/2"));
+    }
+}
diff --git a/core/lib/src/descriptor/mod.rs b/core/lib/src/descriptor/mod.rs
new file mode 100644
index 00000000..d3cb14fe
--- /dev/null
+++ b/core/lib/src/descriptor/mod.rs
@@ -0,0 +1,494 @@
+use std::cell::RefCell;
+use std::collections::BTreeMap;
+use std::convert::{Into, TryFrom};
+use std::fmt;
+use std::str::FromStr;
+
+use bitcoin::blockdata::script::Script;
+use bitcoin::hashes::{hash160, Hash};
+use bitcoin::secp256k1::{All, Secp256k1};
+use bitcoin::util::bip32::{DerivationPath, ExtendedPrivKey, Fingerprint};
+use bitcoin::{PrivateKey, PublicKey};
+
+pub use miniscript::descriptor::Descriptor;
+
+use serde::{Deserialize, Serialize};
+
+pub mod error;
+pub mod extended_key;
+
+pub use self::error::Error;
+pub use self::extended_key::{DerivationIndex, DescriptorExtendedKey};
+
+#[derive(Debug, Clone, Hash, PartialEq, PartialOrd, Eq, Ord, Default)]
+struct DummyKey();
+
+impl fmt::Display for DummyKey {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "DummyKey")
+    }
+}
+
+impl std::str::FromStr for DummyKey {
+    type Err = ();
+
+    fn from_str(_: &str) -> Result<Self, Self::Err> {
+        Ok(DummyKey::default())
+    }
+}
+
+impl miniscript::MiniscriptKey for DummyKey {
+    type Hash = DummyKey;
+
+    fn to_pubkeyhash(&self) -> DummyKey {
+        DummyKey::default()
+    }
+}
+
+pub type DerivedDescriptor = Descriptor<PublicKey>;
+pub type StringDescriptor = Descriptor<String>;
+
+pub trait DescriptorMeta {
+    fn is_witness(&self) -> bool;
+    fn psbt_redeem_script(&self) -> Option<Script>;
+    fn psbt_witness_script(&self) -> Option<Script>;
+}
+
+impl<T> DescriptorMeta for Descriptor<T>
+where
+    T: miniscript::MiniscriptKey + miniscript::ToPublicKey,
+{
+    fn is_witness(&self) -> bool {
+        match self {
+            Descriptor::Bare(_) | Descriptor::Pk(_) | Descriptor::Pkh(_) | Descriptor::Sh(_) => {
+                false
+            }
+            Descriptor::Wpkh(_)
+            | Descriptor::ShWpkh(_)
+            | Descriptor::Wsh(_)
+            | Descriptor::ShWsh(_) => true,
+        }
+    }
+
+    fn psbt_redeem_script(&self) -> Option<Script> {
+        match self {
+            Descriptor::ShWpkh(ref pk) => {
+                let addr =
+                    bitcoin::Address::p2shwpkh(&pk.to_public_key(), bitcoin::Network::Bitcoin);
+                Some(addr.script_pubkey())
+            }
+            Descriptor::ShWsh(ref script) => Some(script.encode().to_v0_p2wsh()),
+            Descriptor::Sh(ref script) => Some(script.encode()),
+            _ => None,
+        }
+    }
+
+    fn psbt_witness_script(&self) -> Option<Script> {
+        match self {
+            Descriptor::Wsh(ref script) => Some(script.encode()),
+            _ => None,
+        }
+    }
+}
+
+trait Key: std::fmt::Debug {
+    fn fingerprint(&self, secp: &Secp256k1<All>) -> Option<Fingerprint>;
+    fn as_public_key(&self, secp: &Secp256k1<All>, index: Option<u32>) -> Result<PublicKey, Error>;
+    fn as_secret_key(
+        &self,
+        secp: &Secp256k1<All>,
+        index: Option<u32>,
+    ) -> Result<Option<PrivateKey>, Error>;
+    fn xprv(&self) -> Option<ExtendedPrivKey>;
+    fn full_path(&self, index: u32) -> Option<DerivationPath>;
+    fn is_fixed(&self) -> bool;
+}
+
+impl Key for PublicKey {
+    fn fingerprint(&self, _secp: &Secp256k1<All>) -> Option<Fingerprint> {
+        None
+    }
+
+    fn as_public_key(
+        &self,
+        _secp: &Secp256k1<All>,
+        _index: Option<u32>,
+    ) -> Result<PublicKey, Error> {
+        Ok(PublicKey::clone(self))
+    }
+
+    fn as_secret_key(
+        &self,
+        _secp: &Secp256k1<All>,
+        _index: Option<u32>,
+    ) -> Result<Option<PrivateKey>, Error> {
+        Ok(None)
+    }
+
+    fn xprv(&self) -> Option<ExtendedPrivKey> {
+        None
+    }
+
+    fn full_path(&self, _index: u32) -> Option<DerivationPath> {
+        None
+    }
+
+    fn is_fixed(&self) -> bool {
+        true
+    }
+}
+
+impl Key for PrivateKey {
+    fn fingerprint(&self, _secp: &Secp256k1<All>) -> Option<Fingerprint> {
+        None
+    }
+
+    fn as_public_key(
+        &self,
+        secp: &Secp256k1<All>,
+        _index: Option<u32>,
+    ) -> Result<PublicKey, Error> {
+        Ok(self.public_key(secp))
+    }
+
+    fn as_secret_key(
+        &self,
+        _secp: &Secp256k1<All>,
+        _index: Option<u32>,
+    ) -> Result<Option<PrivateKey>, Error> {
+        Ok(Some(PrivateKey::clone(self)))
+    }
+
+    fn xprv(&self) -> Option<ExtendedPrivKey> {
+        None
+    }
+
+    fn full_path(&self, _index: u32) -> Option<DerivationPath> {
+        None
+    }
+
+    fn is_fixed(&self) -> bool {
+        true
+    }
+}
+
+impl Key for DescriptorExtendedKey {
+    fn fingerprint(&self, secp: &Secp256k1<All>) -> Option<Fingerprint> {
+        Some(self.root_xpub(secp).fingerprint())
+    }
+
+    fn as_public_key(&self, secp: &Secp256k1<All>, index: Option<u32>) -> Result<PublicKey, Error> {
+        Ok(self.derive_xpub(secp, index.unwrap_or(0))?.public_key)
+    }
+
+    fn as_secret_key(
+        &self,
+        secp: &Secp256k1<All>,
+        index: Option<u32>,
+    ) -> Result<Option<PrivateKey>, Error> {
+        if self.secret.is_none() {
+            return Ok(None);
+        }
+
+        let derivation_path = self.full_path(index.unwrap_or(0));
+        Ok(Some(
+            self.secret
+                .unwrap()
+                .derive_priv(secp, &derivation_path)?
+                .private_key,
+        ))
+    }
+
+    fn xprv(&self) -> Option<ExtendedPrivKey> {
+        self.secret
+    }
+
+    fn full_path(&self, index: u32) -> Option<DerivationPath> {
+        Some(self.full_path(index))
+    }
+
+    fn is_fixed(&self) -> bool {
+        self.final_index == DerivationIndex::Fixed
+    }
+}
+
+#[serde(try_from = "&str", into = "String")]
+#[derive(Debug, Serialize, Deserialize)]
+pub struct ExtendedDescriptor {
+    #[serde(flatten)]
+    internal: StringDescriptor,
+
+    #[serde(skip)]
+    keys: BTreeMap<String, Box<dyn Key>>,
+
+    #[serde(skip)]
+    ctx: Secp256k1<All>,
+}
+
+impl std::clone::Clone for ExtendedDescriptor {
+    fn clone(&self) -> Self {
+        Self {
+            internal: self.internal.clone(),
+            ctx: self.ctx.clone(),
+            keys: BTreeMap::new(),
+        }
+    }
+}
+
+impl ExtendedDescriptor {
+    fn parse_string(string: &str) -> Result<(String, Box<dyn Key>), Error> {
+        if let Ok(pk) = PublicKey::from_str(string) {
+            return Ok((string.to_string(), Box::new(pk)));
+        } else if let Ok(sk) = PrivateKey::from_wif(string) {
+            return Ok((string.to_string(), Box::new(sk)));
+        } else if let Ok(ext_key) = DescriptorExtendedKey::from_str(string) {
+            return Ok((string.to_string(), Box::new(ext_key)));
+        }
+
+        return Err(Error::KeyParsingError(string.to_string()));
+    }
+
+    fn new(sd: StringDescriptor) -> Result<Self, Error> {
+        let ctx = Secp256k1::gen_new();
+        let keys: RefCell<BTreeMap<String, Box<dyn Key>>> = RefCell::new(BTreeMap::new());
+
+        let translatefpk = |string: &String| -> Result<_, Error> {
+            let (key, parsed) = Self::parse_string(string)?;
+            keys.borrow_mut().insert(key, parsed);
+
+            Ok(DummyKey::default())
+        };
+        let translatefpkh = |string: &String| -> Result<_, Error> {
+            let (key, parsed) = Self::parse_string(string)?;
+            keys.borrow_mut().insert(key, parsed);
+
+            Ok(DummyKey::default())
+        };
+
+        sd.translate_pk(translatefpk, translatefpkh)?;
+
+        Ok(ExtendedDescriptor {
+            internal: sd,
+            keys: keys.into_inner(),
+            ctx,
+        })
+    }
+
+    pub fn derive(&self, index: u32) -> Result<DerivedDescriptor, Error> {
+        let translatefpk = |xpub: &String| {
+            self.keys
+                .get(xpub)
+                .unwrap()
+                .as_public_key(&self.ctx, Some(index))
+        };
+        let translatefpkh =
+            |xpub: &String| Ok(hash160::Hash::hash(&translatefpk(xpub)?.to_bytes()));
+
+        Ok(self.internal.translate_pk(translatefpk, translatefpkh)?)
+    }
+
+    pub fn get_xprv(&self) -> Vec<ExtendedPrivKey> {
+        self.keys
+            .iter()
+            .filter(|(_, v)| v.xprv().is_some())
+            .map(|(_, v)| v.xprv().unwrap())
+            .collect()
+    }
+
+    pub fn get_hd_keypaths(
+        &self,
+        index: u32,
+    ) -> Result<BTreeMap<PublicKey, (Fingerprint, DerivationPath)>, Error> {
+        let mut answer = BTreeMap::new();
+
+        for (_, key) in &self.keys {
+            if let Some(fingerprint) = key.fingerprint(&self.ctx) {
+                let derivation_path = key.full_path(index).unwrap();
+                let pubkey = key.as_public_key(&self.ctx, Some(index))?;
+
+                answer.insert(pubkey, (fingerprint, derivation_path));
+            }
+        }
+
+        Ok(answer)
+    }
+
+    pub fn max_satisfaction_weight(&self) -> usize {
+        let fake_pk = PublicKey::from_slice(&[
+            2, 140, 40, 169, 123, 248, 41, 139, 192, 210, 61, 140, 116, 148, 82, 163, 46, 105, 75,
+            101, 227, 10, 148, 114, 163, 149, 74, 179, 15, 229, 50, 76, 170,
+        ])
+        .unwrap();
+        let translated: Descriptor<PublicKey> = self
+            .internal
+            .translate_pk(
+                |_| -> Result<_, ()> { Ok(fake_pk.clone()) },
+                |_| -> Result<_, ()> { Ok(Default::default()) },
+            )
+            .unwrap();
+
+        translated.max_satisfaction_weight()
+    }
+
+    pub fn is_fixed(&self) -> bool {
+        self.keys.iter().all(|(_, key)| key.is_fixed())
+    }
+}
+
+impl TryFrom<&str> for ExtendedDescriptor {
+    type Error = Error;
+
+    fn try_from(value: &str) -> Result<Self, Self::Error> {
+        let internal = StringDescriptor::from_str(value)?;
+        ExtendedDescriptor::new(internal)
+    }
+}
+
+impl TryFrom<StringDescriptor> for ExtendedDescriptor {
+    type Error = Error;
+
+    fn try_from(other: StringDescriptor) -> Result<Self, Self::Error> {
+        ExtendedDescriptor::new(other)
+    }
+}
+
+impl FromStr for ExtendedDescriptor {
+    type Err = Error;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        Self::try_from(s)
+    }
+}
+
+impl Into<String> for ExtendedDescriptor {
+    fn into(self) -> String {
+        format!("{}", self.internal)
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use std::str::FromStr;
+
+    use bitcoin::hashes::hex::FromHex;
+    use bitcoin::{Network, PublicKey};
+
+    use crate::descriptor::*;
+
+    macro_rules! hex_fingerprint {
+        ($hex:expr) => {
+            Fingerprint::from_hex($hex).unwrap()
+        };
+    }
+
+    macro_rules! hex_pubkey {
+        ($hex:expr) => {
+            PublicKey::from_str($hex).unwrap()
+        };
+    }
+
+    macro_rules! deriv_path {
+        ($str:expr) => {
+            DerivationPath::from_str($str).unwrap()
+        };
+
+        () => {
+            DerivationPath::from(vec![])
+        };
+    }
+
+    #[test]
+    fn test_descriptor_parse_wif() {
+        let string = "pkh(cVt4o7BGAig1UXywgGSmARhxMdzP5qvQsxKkSsc1XEkw3tDTQFpy)";
+        let desc = ExtendedDescriptor::from_str(string).unwrap();
+        assert!(desc.is_fixed());
+        assert_eq!(
+            desc.derive(0)
+                .unwrap()
+                .address(Network::Testnet)
+                .unwrap()
+                .to_string(),
+            "mqwpxxvfv3QbM8PU8uBx2jaNt9btQqvQNx"
+        );
+        assert_eq!(
+            desc.derive(42)
+                .unwrap()
+                .address(Network::Testnet)
+                .unwrap()
+                .to_string(),
+            "mqwpxxvfv3QbM8PU8uBx2jaNt9btQqvQNx"
+        );
+        assert_eq!(desc.get_secret_keys().len(), 1);
+    }
+
+    #[test]
+    fn test_descriptor_parse_pubkey() {
+        let string = "pkh(039b6347398505f5ec93826dc61c19f47c66c0283ee9be980e29ce325a0f4679ef)";
+        let desc = ExtendedDescriptor::from_str(string).unwrap();
+        assert!(desc.is_fixed());
+        assert_eq!(
+            desc.derive(0)
+                .unwrap()
+                .address(Network::Testnet)
+                .unwrap()
+                .to_string(),
+            "mqwpxxvfv3QbM8PU8uBx2jaNt9btQqvQNx"
+        );
+        assert_eq!(
+            desc.derive(42)
+                .unwrap()
+                .address(Network::Testnet)
+                .unwrap()
+                .to_string(),
+            "mqwpxxvfv3QbM8PU8uBx2jaNt9btQqvQNx"
+        );
+        assert_eq!(desc.get_secret_keys().len(), 0);
+    }
+
+    #[test]
+    fn test_descriptor_parse_xpub() {
+        let string = "pkh(tpubDEnoLuPdBep9bzw5LoGYpsxUQYheRQ9gcgrJhJEcdKFB9cWQRyYmkCyRoTqeD4tJYiVVgt6A3rN6rWn9RYhR9sBsGxji29LYWHuKKbdb1ev/*)";
+        let desc = ExtendedDescriptor::from_str(string).unwrap();
+        assert!(!desc.is_fixed());
+        assert_eq!(
+            desc.derive(0)
+                .unwrap()
+                .address(Network::Testnet)
+                .unwrap()
+                .to_string(),
+            "mxbXpnVkwARGtYXk5yeGYf59bGWuPpdE4X"
+        );
+        assert_eq!(
+            desc.derive(42)
+                .unwrap()
+                .address(Network::Testnet)
+                .unwrap()
+                .to_string(),
+            "mhtuS1QaEV4HPcK4bWk4Wvpd64SUjiC5Zt"
+        );
+        assert_eq!(desc.get_xprv().len(), 0);
+    }
+
+    #[test]
+    #[should_panic(expected = "KeyParsingError")]
+    fn test_descriptor_parse_fail() {
+        let string = "pkh(this_is_not_a_valid_key)";
+        ExtendedDescriptor::from_str(string).unwrap();
+    }
+
+    #[test]
+    fn test_descriptor_hd_keypaths() {
+        let string = "pkh(tpubDEnoLuPdBep9bzw5LoGYpsxUQYheRQ9gcgrJhJEcdKFB9cWQRyYmkCyRoTqeD4tJYiVVgt6A3rN6rWn9RYhR9sBsGxji29LYWHuKKbdb1ev/*)";
+        let desc = ExtendedDescriptor::from_str(string).unwrap();
+        let keypaths = desc.get_hd_keypaths(0).unwrap();
+        assert!(keypaths.contains_key(&hex_pubkey!(
+            "025d5fc65ebb8d44a5274b53bac21ff8307fec2334a32df05553459f8b1f7fe1b6"
+        )));
+        assert_eq!(
+            keypaths.get(&hex_pubkey!(
+                "025d5fc65ebb8d44a5274b53bac21ff8307fec2334a32df05553459f8b1f7fe1b6"
+            )),
+            Some(&(hex_fingerprint!("31a507b8"), deriv_path!("m/0")))
+        )
+    }
+}
diff --git a/core/lib/src/error.rs b/core/lib/src/error.rs
new file mode 100644
index 00000000..78c6c571
--- /dev/null
+++ b/core/lib/src/error.rs
@@ -0,0 +1,21 @@
+#[derive(Debug)]
+pub enum Error {
+    KeyMismatch(bitcoin::secp256k1::PublicKey, bitcoin::secp256k1::PublicKey),
+    MissingInputUTXO(usize),
+
+    BIP32(bitcoin::util::bip32::Error),
+    Secp256k1(bitcoin::secp256k1::Error),
+}
+
+macro_rules! impl_error {
+    ( $from:ty, $to:ident ) => {
+        impl std::convert::From<$from> for Error {
+            fn from(err: $from) -> Self {
+                Error::$to(err)
+            }
+        }
+    };
+}
+
+impl_error!(bitcoin::util::bip32::Error, BIP32);
+impl_error!(bitcoin::secp256k1::Error, Secp256k1);
diff --git a/core/lib/src/lib.rs b/core/lib/src/lib.rs
index 31e1bb20..16d34ebe 100644
--- a/core/lib/src/lib.rs
+++ b/core/lib/src/lib.rs
@@ -1,7 +1,8 @@
-#[cfg(test)]
-mod tests {
-    #[test]
-    fn it_works() {
-        assert_eq!(2 + 2, 4);
-    }
-}
+pub extern crate bitcoin;
+extern crate log;
+pub extern crate miniscript;
+extern crate serde;
+extern crate serde_json;
+
+pub mod descriptor;
+pub mod error;
diff --git a/core/lib/src/psbt.rs b/core/lib/src/psbt.rs
new file mode 100644
index 00000000..2326e758
--- /dev/null
+++ b/core/lib/src/psbt.rs
@@ -0,0 +1,198 @@
+use std::collections::BTreeMap;
+
+use bitcoin::hashes::Hash;
+use bitcoin::util::bip143::SighashComponents;
+use bitcoin::util::bip32::{DerivationPath, ExtendedPrivKey, Fingerprint};
+use bitcoin::util::psbt;
+use bitcoin::{PrivateKey, PublicKey, Script, SigHashType, Transaction};
+
+use bitcoin::secp256k1::{self, All, Message, Secp256k1};
+
+use miniscript::{BitcoinSig, Satisfier};
+
+use crate::descriptor::ExtendedDescriptor;
+use crate::error::Error;
+use crate::signer::Signer;
+
+pub struct PSBTSatisfier<'a> {
+    input: &'a psbt::Input,
+    create_height: Option<u32>,
+    current_height: Option<u32>,
+}
+
+impl<'a> PSBTSatisfier<'a> {
+    pub fn new(
+        input: &'a psbt::Input,
+        create_height: Option<u32>,
+        current_height: Option<u32>,
+    ) -> Self {
+        PSBTSatisfier {
+            input,
+            create_height,
+            current_height,
+        }
+    }
+}
+
+// TODO: also support hash preimages through the "unknown" section of PSBT
+impl<'a> Satisfier<bitcoin::PublicKey> for PSBTSatisfier<'a> {
+    // from https://docs.rs/miniscript/0.12.0/src/miniscript/psbt/mod.rs.html#96
+    fn lookup_sig(&self, pk: &bitcoin::PublicKey) -> Option<BitcoinSig> {
+        if let Some(rawsig) = self.input.partial_sigs.get(pk) {
+            let (flag, sig) = rawsig.split_last().unwrap();
+            let flag = bitcoin::SigHashType::from_u32(*flag as u32);
+            let sig = match secp256k1::Signature::from_der(sig) {
+                Ok(sig) => sig,
+                Err(..) => return None,
+            };
+            Some((sig, flag))
+        } else {
+            None
+        }
+    }
+
+    fn check_older(&self, height: u32) -> bool {
+        // TODO: test >= / >
+        self.current_height.unwrap_or(0) >= self.create_height.unwrap_or(0) + height
+    }
+
+    fn check_after(&self, height: u32) -> bool {
+        self.current_height.unwrap_or(0) > height
+    }
+}
+
+#[derive(Debug)]
+pub struct PSBTSigner<'a> {
+    tx: &'a Transaction,
+    secp: Secp256k1<All>,
+
+    // psbt: &'b psbt::PartiallySignedTransaction,
+    extended_keys: BTreeMap<Fingerprint, ExtendedPrivKey>,
+    private_keys: BTreeMap<PublicKey, PrivateKey>,
+}
+
+impl<'a> PSBTSigner<'a> {
+    pub fn from_descriptor(tx: &'a Transaction, desc: &ExtendedDescriptor) -> Result<Self, Error> {
+        let secp = Secp256k1::gen_new();
+
+        let mut extended_keys = BTreeMap::new();
+        for xprv in desc.get_xprv() {
+            let fing = xprv.fingerprint(&secp);
+            extended_keys.insert(fing, xprv);
+        }
+
+        let mut private_keys = BTreeMap::new();
+        for privkey in desc.get_secret_keys() {
+            let pubkey = privkey.public_key(&secp);
+            private_keys.insert(pubkey, privkey);
+        }
+
+        Ok(PSBTSigner {
+            tx,
+            secp,
+            extended_keys,
+            private_keys,
+        })
+    }
+}
+
+impl<'a> Signer for PSBTSigner<'a> {
+    fn sig_legacy_from_fingerprint(
+        &self,
+        index: usize,
+        sighash: SigHashType,
+        fingerprint: &Fingerprint,
+        path: &DerivationPath,
+        script: &Script,
+    ) -> Result<Option<BitcoinSig>, Error> {
+        self.extended_keys
+            .get(fingerprint)
+            .map_or(Ok(None), |xprv| {
+                let privkey = xprv.derive_priv(&self.secp, path)?;
+                // let derived_pubkey = secp256k1::PublicKey::from_secret_key(&self.secp, &privkey.private_key.key);
+
+                let hash = self.tx.signature_hash(index, script, sighash.as_u32());
+
+                let signature = self.secp.sign(
+                    &Message::from_slice(&hash.into_inner()[..])?,
+                    &privkey.private_key.key,
+                );
+
+                Ok(Some((signature, sighash)))
+            })
+    }
+
+    fn sig_legacy_from_pubkey(
+        &self,
+        index: usize,
+        sighash: SigHashType,
+        public_key: &PublicKey,
+        script: &Script,
+    ) -> Result<Option<BitcoinSig>, Error> {
+        self.private_keys
+            .get(public_key)
+            .map_or(Ok(None), |privkey| {
+                let hash = self.tx.signature_hash(index, script, sighash.as_u32());
+
+                let signature = self
+                    .secp
+                    .sign(&Message::from_slice(&hash.into_inner()[..])?, &privkey.key);
+
+                Ok(Some((signature, sighash)))
+            })
+    }
+
+    fn sig_segwit_from_fingerprint(
+        &self,
+        index: usize,
+        sighash: SigHashType,
+        fingerprint: &Fingerprint,
+        path: &DerivationPath,
+        script: &Script,
+        value: u64,
+    ) -> Result<Option<BitcoinSig>, Error> {
+        self.extended_keys
+            .get(fingerprint)
+            .map_or(Ok(None), |xprv| {
+                let privkey = xprv.derive_priv(&self.secp, path)?;
+
+                let hash = SighashComponents::new(self.tx).sighash_all(
+                    &self.tx.input[index],
+                    script,
+                    value,
+                );
+
+                let signature = self.secp.sign(
+                    &Message::from_slice(&hash.into_inner()[..])?,
+                    &privkey.private_key.key,
+                );
+
+                Ok(Some((signature, sighash)))
+            })
+    }
+
+    fn sig_segwit_from_pubkey(
+        &self,
+        index: usize,
+        sighash: SigHashType,
+        public_key: &PublicKey,
+        script: &Script,
+        value: u64,
+    ) -> Result<Option<BitcoinSig>, Error> {
+        self.private_keys
+            .get(public_key)
+            .map_or(Ok(None), |privkey| {
+                let hash = SighashComponents::new(self.tx).sighash_all(
+                    &self.tx.input[index],
+                    script,
+                    value,
+                );
+
+                let signature = self
+                    .secp
+                    .sign(&Message::from_slice(&hash.into_inner()[..])?, &privkey.key);
+
+                Ok(Some((signature, sighash)))
+            })
+    }
+}
diff --git a/core/lib/src/signer.rs b/core/lib/src/signer.rs
new file mode 100644
index 00000000..8f6f8b6e
--- /dev/null
+++ b/core/lib/src/signer.rs
@@ -0,0 +1,87 @@
+use bitcoin::util::bip32::{DerivationPath, Fingerprint};
+use bitcoin::{PublicKey, Script, SigHashType};
+
+use miniscript::miniscript::satisfy::BitcoinSig;
+
+use crate::error::Error;
+
+pub trait Signer {
+    fn sig_legacy_from_fingerprint(
+        &self,
+        index: usize,
+        sighash: SigHashType,
+        fingerprint: &Fingerprint,
+        path: &DerivationPath,
+        script: &Script,
+    ) -> Result<Option<BitcoinSig>, Error>;
+    fn sig_legacy_from_pubkey(
+        &self,
+        index: usize,
+        sighash: SigHashType,
+        public_key: &PublicKey,
+        script: &Script,
+    ) -> Result<Option<BitcoinSig>, Error>;
+
+    fn sig_segwit_from_fingerprint(
+        &self,
+        index: usize,
+        sighash: SigHashType,
+        fingerprint: &Fingerprint,
+        path: &DerivationPath,
+        script: &Script,
+        value: u64,
+    ) -> Result<Option<BitcoinSig>, Error>;
+    fn sig_segwit_from_pubkey(
+        &self,
+        index: usize,
+        sighash: SigHashType,
+        public_key: &PublicKey,
+        script: &Script,
+        value: u64,
+    ) -> Result<Option<BitcoinSig>, Error>;
+}
+
+#[allow(dead_code)]
+impl dyn Signer {
+    fn sig_legacy_from_fingerprint(
+        &self,
+        _index: usize,
+        _sighash: SigHashType,
+        _fingerprint: &Fingerprint,
+        _path: &DerivationPath,
+        _script: &Script,
+    ) -> Result<Option<BitcoinSig>, Error> {
+        Ok(None)
+    }
+    fn sig_legacy_from_pubkey(
+        &self,
+        _index: usize,
+        _sighash: SigHashType,
+        _public_key: &PublicKey,
+        _script: &Script,
+    ) -> Result<Option<BitcoinSig>, Error> {
+        Ok(None)
+    }
+
+    fn sig_segwit_from_fingerprint(
+        &self,
+        _index: usize,
+        _sighash: SigHashType,
+        _fingerprint: &Fingerprint,
+        _path: &DerivationPath,
+        _script: &Script,
+        _value: u64,
+    ) -> Result<Option<BitcoinSig>, Error> {
+        Ok(None)
+    }
+    fn sig_segwit_from_pubkey(
+        &self,
+        _index: usize,
+        _sighash: SigHashType,
+        _public_key: &PublicKey,
+        _script: &Script,
+        _value: u64,
+    ) -> Result<Option<BitcoinSig>, Error> {
+        Ok(None)
+    }
+}